Rename MediaEntry.uploader() to .get_uploader()

The .uploader() method conflicts with the uploader database
field. As we're moving to .FIELD for db field access, this
is a relevant conflict.

So renaming .uploader() to .get_uploader()

mediagoblin/listings/views.py

@@ -86,7 +86,7 @@ def tag_atom_feed(request):
         feed.add(entry.get('title'),
             entry.get('description_html'),
             content_type='html',
-            author=entry.uploader()['username'],
+            author=entry.get_uploader()['username'],
             updated=entry.get('created'),
             url=entry.url_for_self(request.urlgen))