rework panning -- Squashed commit of the following:

commit 6f4f4f161b00cb36252727f67ecc4913eb944fd7
Author: Robin Gareus <robin@gareus.org>
Date:   Wed Jan 8 22:13:09 2014 +0100

    fix panner plugin discovery (prev commit)

commit 26e514f4a80af9192cae3cbd62fde0ae95474dfc
Author: Robin Gareus <robin@gareus.org>
Date:   Wed Jan 8 18:56:59 2014 +0100

    update panner plugin discovery

    * recurse dirs in 'PANNER_PATH' and 'panner_dir_name' up to 1 level.
    * don't look in ardour_dll_directory() -- no panners are supposed to be in there
    * use .dylib on OSX exclusively.

commit a514c3f1c425dccf3d42eee9d2b183b44fd26a03
Author: Robin Gareus <robin@gareus.org>
Date:   Wed Jan 8 16:48:34 2014 +0100

    remove debug/devel printf()s

commit d863742ddc69af493ee6a8817bc778968d9b0800
Author: Robin Gareus <robin@gareus.org>
Date:   Wed Jan 8 16:17:13 2014 +0100

    panner-type: session backward/forward compatibility

commit 25d5e4c663ada34129451b0f9045ab047d6cc2f0
Author: Robin Gareus <robin@gareus.org>
Date:   Wed Jan 8 16:09:07 2014 +0100

    update URIs -> URLs

commit 00a606a43d9456cfbaf43cae4fb598549326ba71
Merge: 0f1cec1 382eb0f
Author: Robin Gareus <robin@gareus.org>
Date:   Wed Jan 8 03:29:45 2014 +0100

    Merge branch 'master' into panning

commit 0f1cec19babae538c9697eed4be5d6ddc851b013
Author: Robin Gareus <robin@gareus.org>
Date:   Wed Jan 8 02:41:15 2014 +0100

    switch panner ID to URI

commit 575282b412c3ae1cd8219cf75f00a1a4239e2813
Author: Robin Gareus <robin@gareus.org>
Date:   Wed Jan 8 00:50:15 2014 +0100

    prepare API for panner URI

commit ea62cd049308859782a7bb16e4f18169d8638b46
Author: Robin Gareus <robin@gareus.org>
Date:   Tue Jan 7 19:57:06 2014 +0100

    update development doc relating to panner selection

commit 586d7de2392e26b9d7f597b1a00b98dfaa42ecdc
Author: Robin Gareus <robin@gareus.org>
Date:   Tue Jan 7 19:56:24 2014 +0100

    clean up PanShell::set_user_selected_panner_type() API

commit 99077886a5a1cacece908d87c29c3be12903027e
Author: Robin Gareus <robin@gareus.org>
Date:   Tue Jan 7 04:46:22 2014 +0100

    panner bypass: visualize & [in]sensitivity

commit 46d688d216f0e67d672376a607157af02b359fb2
Merge: 4e67573 c4cdf61
Author: Robin Gareus <robin@gareus.org>
Date:   Tue Jan 7 02:18:54 2014 +0100

    Merge branch 'master' into panning

commit 4e67573517b3d60ddf65729783687b16cfb2adb7
Author: Robin Gareus <robin@gareus.org>
Date:   Tue Jan 7 01:05:17 2014 +0100

    don't call configure_io() for merely swapping panners

commit d32a4c51f6967f48f7680554866f1f7b311ccde1
Merge: a3226d4 cec3116
Author: Robin Gareus <robin@gareus.org>
Date:   Mon Jan 6 23:49:55 2014 +0100

    Merge branch 'master' into panning

commit a3226d46b598afae54a65ac69320eca84669f347
Author: Robin Gareus <robin@gareus.org>
Date:   Mon Jan 6 17:52:38 2014 +0100

    add notes about panner re-design

commit d1ae2366024605f22b05572a81ee249e6fdbcd2f
Author: Robin Gareus <robin@gareus.org>
Date:   Mon Jan 6 15:06:40 2014 +0100

    add simple stereo-balance panner for testing

commit e0ddd256ff2288b8d8cfad3ad485a916964ce5b5
Author: Robin Gareus <robin@gareus.org>
Date:   Mon Jan 6 17:02:52 2014 +0100

    add frontend/GUI for panner selection

commit 2cb8f846755eb5aea8a2620d31ea981c446c4041
Author: Robin Gareus <robin@gareus.org>
Date:   Mon Jan 6 17:02:20 2014 +0100

    prepare backend for panner selection

1 files changed, 42 insertions, 15 deletions

diff --git a/libs/ardour/panner_manager.cc b/libs/ardour/panner_manager.cc
index 94e8d4ff2f..b62f36b355 100644
--- a/libs/ardour/panner_manager.cc
+++ b/libs/ardour/panner_manager.cc
@@ -24,7 +24,8 @@
 
 #include "pbd/error.h"
 #include "pbd/compose.h"
-#include "pbd/file_utils.h"
+#include "pbd/pathscanner.h"
+#include "pbd/stl_delete.h"
 
 #include "ardour/debug.h"
 #include "ardour/panner_manager.h"
@@ -59,25 +60,30 @@ PannerManager::instance ()
 	return *_instance;
 }
 
+static bool panner_filter (const string& str, void */*arg*/)
+{
+#ifdef __APPLE__
+	return str[0] != '.' && (str.length() > 6 && str.find (".dylib") == (str.length() - 6));
+#else
+	return str[0] != '.' && (str.length() > 3 && str.find (".so") == (str.length() - 3));
+#endif
+}
+
 void
 PannerManager::discover_panners ()
 {
-	vector<std::string> panner_modules;
-
-	Glib::PatternSpec so_extension_pattern("*.so");
-	Glib::PatternSpec dylib_extension_pattern("*.dylib");
+	PathScanner scanner;
+	std::vector<std::string *> *panner_modules;
+	std::string search_path = panner_search_path().to_string();
 
-	find_matching_files_in_search_path (panner_search_path (),
-	                                    so_extension_pattern, panner_modules);
+	DEBUG_TRACE (DEBUG::Panning, string_compose (_("looking for panners in %1\n"), search_path));
 
-	find_matching_files_in_search_path (panner_search_path (),
-	                                    dylib_extension_pattern, panner_modules);
+	panner_modules = scanner (search_path, panner_filter, 0, false, true, 1, true);
 
-	DEBUG_TRACE (DEBUG::Panning, string_compose (_("looking for panners in %1"), panner_search_path().to_string()));
-
-	for (vector<std::string>::iterator i = panner_modules.begin(); i != panner_modules.end(); ++i) {
-		panner_discover (*i);
+	for (vector<std::string *>::iterator i = panner_modules->begin(); i != panner_modules->end(); ++i) {
+		panner_discover (**i);
 	}
+	vector_delete (panner_modules);
 }
 
 int
@@ -97,7 +103,7 @@ PannerManager::panner_discover (string path)
 
 		if (i == panner_info.end()) {
 			panner_info.push_back (pinfo);
-			DEBUG_TRACE (DEBUG::Panning, string_compose(_("Panner discovered: \"%1\" in %2"), pinfo->descriptor.name, path));
+			DEBUG_TRACE (DEBUG::Panning, string_compose(_("Panner discovered: \"%1\" in %2\n"), pinfo->descriptor.name, path));
 		}
 	}
 
@@ -138,12 +144,21 @@ PannerManager::get_descriptor (string path)
 }
 
 PannerInfo*
-PannerManager::select_panner (ChanCount in, ChanCount out)
+PannerManager::select_panner (ChanCount in, ChanCount out, std::string const uri)
 {
 	PanPluginDescriptor* d;
 	int32_t nin = in.n_audio();
 	int32_t nout = out.n_audio();
 
+	/* look for user-preference -- check if channels match */
+	for (list<PannerInfo*>::iterator p = panner_info.begin(); p != panner_info.end(); ++p) {
+		d = &(*p)->descriptor;
+		if (d->panner_uri != uri) continue;
+		if (d->in != nin && d->in != -1) continue;
+		if (d->out != nout && d->out != -1) continue;
+		return *p;
+	}
+
 	/* look for exact match first */
 
 	for (list<PannerInfo*>::iterator p = panner_info.begin(); p != panner_info.end(); ++p) {
@@ -188,3 +203,15 @@ PannerManager::select_panner (ChanCount in, ChanCount out)
 
 	return 0;
 }
+
+PannerInfo*
+PannerManager::get_by_uri (std::string uri)
+{
+	PannerInfo* pi = NULL;
+	for (list<PannerInfo*>::iterator p = panner_info.begin(); p != panner_info.end(); ++p) {
+		if ((*p)->descriptor.panner_uri != uri) continue;
+		pi = (*p);
+		break;
+	}
+	return pi;
+}