Rewrote id3Dup to search for tags manually.  Now libid3tag will actually tell us the version of the tag we got.  As an added benefit we also do fewer reads/mallocs when scanning mp3s during database update/creation.

git-svn-id: https://svn.musicpd.org/mpd/trunk@4277 09075e82-0dd4-0310-85a5-a0d7c8717e4f