addon improvements/fixes

- better error reporting when an addon fails to load
- upload an addon which loads partly but then fails (eg, module loads but class register fails)
- bugfix addon loading, failier to load would leave _bpy_types._register_immediate = False
- added which change on disk are reloaded when enabling.
- bpy.path.module_names() now returns (module_name, module_path) pairs.

release/scripts/modules/bpy/utils.py

@@ -70,7 +70,7 @@ def modules_from_path(path, loaded_modules):
 
     modules = []
 
-    for mod_name in _bpy.path.module_names(path):
+    for mod_name, mod_path in _bpy.path.module_names(path):
         mod = _test_import(mod_name, loaded_modules)
         if mod:
             modules.append(mod)