Updated the gwt.junit and gwt.javac for user tests to get access to shared test code from dev/core/test.  Fixes build break at r2857.

Review by: freeland (desk check)

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@2858 8db76d5a-ed1c-0410-87a9-c151d255dfc7