Don't allow both scrobblers to be loaded simultaneously.

This starts issue #7.

src/scrobbler/plugin.c

@@ -10,6 +10,7 @@
 #include <audacious/misc.h>
 #include <audacious/playlist.h>
 #include <audacious/plugin.h>
+#include <audacious/plugins.h>
 #include <libaudcore/audstrings.h>
 #include <libaudcore/hook.h>
 #include <libaudgui/libaudgui.h>
@@ -137,6 +138,14 @@ void stop(void) {
 
 static gboolean init(void)
 {
+    PluginHandle *new_scrobbler = aud_plugin_lookup_basename("scrobbler2");
+    if (new_scrobbler != NULL && aud_plugin_get_enabled(new_scrobbler)) {
+        aud_interface_show_error(N_("This is an old, legacy version of the Scrobbler plugin.\n"
+                                    "To use it, disable the Scrobbler 2.0 plugin."));
+        return FALSE;
+    }
+
+
     start();
     return TRUE;
 }

src/scrobbler2/scrobbler.c

@@ -7,13 +7,17 @@
  * It is licensed under the GNU General Public License, version 3.
  */
 
+//TODO: this is to be removed when the old scrobbler is deprecated
+#include <audacious/plugins.h>
+
 //audacious includes
 #include <config.h>
 #include <audacious/plugin.h>
 #include <audacious/drct.h>
 #include <audacious/playlist.h>
 #include <libaudcore/hook.h>
 
+
 //plugin includes
 #include "scrobbler.h"
 
@@ -209,7 +213,14 @@ static void unpaused (void *hook_data, void *user_data) {
     play_started_at = g_get_monotonic_time();
 }
 
+
+
 static bool_t scrobbler_init (void) {
+    PluginHandle *old_scrobbler = aud_plugin_lookup_basename("scrobbler");
+    if (old_scrobbler != NULL && aud_plugin_get_enabled(old_scrobbler)) {
+        aud_plugin_enable(old_scrobbler, FALSE);
+    }
+
     // Initialize libXML and check potential ABI mismatches between
     // the version it was compiled for and the actual libXML in use
     LIBXML_TEST_VERSION