Sophist id3v23 matching v2

Second attempt at fixing identification of mis-matched file / MB data in id3v23 mp3 files.

This has been implemented as discussed - [click here](https://github.com/musicbrainz/picard/pull/105) for the previous pull-request 105 and [click here](http://chatlogs.musicbrainz.org/musicbrainz-devel/2013/2013-06/2013-06-02.html#T18-54-59-925059) for a chat-log.