Guard against invalid dispIds in JavaDispatchImpl

Also, rather than write an invalid dispId and wait for things to blow up, throw
a HostedModeException if we hit a JSNI ref that shouldn't be there

Review at http://gwt-code-reviews.appspot.com/1172801

Review by: scottb@google.com

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@9390 8db76d5a-ed1c-0410-87a9-c151d255dfc7
9 files changed