Added api-checker reference jars for 2.6.0


git-svn-id: http://google-web-toolkit.googlecode.com/svn/tools@11662 8db76d5a-ed1c-0410-87a9-c151d255dfc7
Added Guava 16.0.1.



git-svn-id: http://google-web-toolkit.googlecode.com/svn/tools@11664 8db76d5a-ed1c-0410-87a9-c151d255dfc7
Merge remote-tracking branch 'origin/upstream'

Change-Id: I8ca4bbd89be9f95a988b77405645c29c0259cc56