Setup path correctly in testall.py
Setup path correctly in testall.py

By comparing `sys.path` as setup by nose vs. testall.py it seems that we
weren't adding the top-level beets directory to the path. The script was
also previously changing the working directory before running the tests.

jackwilsdon/beets,ibmibmibm/beets,beetbox/beets,shamangeorge/beets,shamangeorge/beets,jackwilsdon/beets,jackwilsdon/beets,beetbox/beets,sampsyo/beets,jackwilsdon/beets,sampsyo/beets,sampsyo/beets,shamangeorge/beets,SusannaMaria/beets,ibmibmibm/beets,SusannaMaria/beets,beetbox/beets,SusannaMaria/beets,sampsyo/beets,SusannaMaria/beets,beetbox/beets,shamangeorge/beets,ibmibmibm/beets,ibmibmibm/beets