most unused arg warnings corrected.

- removed deprecated bitmap arg from IMB_allocImBuf (plugins will need updating).
- mostly tagged UNUSED() since some of these functions look like they may need to have the arguments used later.

source/blender/makesrna/intern/rna_userdef.c

@@ -169,7 +169,7 @@ static PointerRNA rna_UserDef_system_get(PointerRNA *ptr)
 
 static void rna_UserDef_audio_update(Main *bmain, Scene *scene, PointerRNA *ptr)
 {
-	sound_init(bmain);
+	sound_init();
 }
 
 static void rna_Userdef_memcache_update(Main *bmain, Scene *scene, PointerRNA *ptr)