Reviewed in person by Scott Blum.  This assertion was tripped during
CompilerTest, and was made invalid by the hosted mode speedup.  
These changes keep classes around, and this assertion assumes a perfectly
empty set of classes before the beginning of a run.


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@217 8db76d5a-ed1c-0410-87a9-c151d255dfc7