Streamlined metadata caching logic.


git-svn-id: http://music21.googlecode.com/svn/trunk@3569 5c16147e-a200-11de-b0cc-ab0ad15e60d0
fixed parse function for abc and other multiwork paths.

git-svn-id: http://music21.googlecode.com/svn/trunk@3570 5c16147e-a200-11de-b0cc-ab0ad15e60d0