Fixes memory leak in ResourceOracleImpl under GWT Designer.

While using GWT Designer the class path cache in ResourceOracleImpl never gets cleared of obsolete data.

http://gwt-code-reviews.appspot.com/1308801/show
Patch by: amitin
Review by: me


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@9717 8db76d5a-ed1c-0410-87a9-c151d255dfc7