AppEngine uploads were choking on massive cache files written into war/WEB-INF
This change moves the persistent unit cache default dir to war/.. for  DevMode and
Compiler entry points (GWTShell already wrote to .gwt-tmp instead)

Review at http://gwt-code-reviews.appspot.com/1449805


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@10220 8db76d5a-ed1c-0410-87a9-c151d255dfc7