Fixed uncaught mutagen exception.

This is a recent change to mutagen and our code doesn't reflect this
yet. Mutagen can raise a ValueError when it finds an mp3 file to be
unsafe.
IRC info command now defaults to current playing song if none given.

This is also a rewrite of the info command to be more in style of
the new tag command.

Small bug fix in the tags command, it used the regex matched 'id'
when the current song was used rather than the 'song.id'.