Provide a last_currentsong method like last_status
Revert "Merge pull request #34 from eonpatapon/no-polling-2"

Keep polling for now, to detect connection loss during idle (issue #35).
Maybe a better solution will be found in the future.
Add a fallback MPDWrapper.fileno() method (issue #36)

Fedora 17 still ships python-mpd 0.2, which does not have
MPDClient.fileno() – so let's implement it ourselves.
Fix exception name in fallback fileno()
Add other missing methods for issue #36

TODO: This needs to be cleaned up and made more pythonic, but for now,
it works... Also, still need to override the predecesor of _execute().
Override _docommand(). Hopefully this works. (issue #36)