Delegate album_for_id to plugins if no MusicBrainz match is found
Add support for manually entered release ID in Discogs
Determine IDs from MusicBrainz and Discogs URLs
Fix tests for albums from manual ID
Return a list of candidates in hooks._album_for_id
Improve regular expression for Discogs IDs
Fix bug in discogs.album_for_id for ID-Strings that end in a bracket
Make regex for Discogs ID more specific
Merge pull request #291 from jbaiter/discogs_albumid

Support for manually entered IDs in plugins
fix tests for ID parsing (#291)

The previous tests accessed the network. This refactoring lets us test the ID
parsing in isolation.
#291: simplify plugin interface for album_for_id
#291: restore shortcut for manual ID searches
fix implicit ID search

This was broken because hooks._album_for_id now returns a list. This was
assuming it returned a single value (or None).
#291: plugin hook for track_for_id

For symmetry with album candidates, plugins can now provide item candidates by
ID.
#291: changelog and docs
Merge branch 'master' into python26-resub