make media_manager a property of MediaEntry in mixin.py

In all cases where get_media_manager(_media_type_as_string) was called in
our code base we ultimately passed in a "MediaEntry().media_type" to get
the matching MEDIA_MANAGER. It so makes sense to make this a function of
the MediaEntry rather than a global function in mediagoblin.media_types and
passing around media_entry.media_type as arguments all the time.

It saves a few import statements and arguments. I also made it so the
Media_manager property is cached for subsequent calls, although I am not too
sure that this is needed (there are other cases for which this would make
more sense)

Also add a get_media_manager test to the media submission tests. It submits
an image and checks that both media.media_type and media.media_manager
return the right thing. Not sure if these tests could not be merged with an
existing submission test, but it can't hurt to have things explicit.

TODO: Right now we iterate through all existing media_managers to find the
right one based on the string of its module name. This should be made a simple
dict lookup to avoid all the extra work.

Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>

mediagoblin/media_types/__init__.py

@@ -78,25 +78,6 @@ def get_media_managers():
         yield media_type, sys.modules[media_type].MEDIA_MANAGER
 
 
-def get_media_manager(_media_type):
-    '''
-    Get the MEDIA_MANAGER based on a media type string
-
-    Example::
-        get_media_type('mediagoblin.media_types.image')
-    '''
-    if not _media_type:
-        return False
-
-    for media_type, manager in get_media_managers():
-        if media_type in _media_type:
-            return manager
-
-    # Nope?  Then raise an error
-    raise FileTypeNotSupported(
-        "MediaManager not in enabled types.  Check media_types in config?")
-
-
 def get_media_type_and_manager(filename):
     '''
     Try to find the media type based on the file name, extension