Allow properties files for inner classes to use _ as the separator in addition
to $ -- some build tools make it awkward to use $ in file names.  Added tests
for looking up inner classes.

Patch by: jat
Review by: ajr


git-svn-id: https://google-web-toolkit.googlecode.com/svn/releases/1.6@3855 8db76d5a-ed1c-0410-87a9-c151d255dfc7