Ensure RequestFactory is UTF-8 clean.
Refactor existing RPC Unicode tests to allow re-use by RequestFactory.
Issue 5474.
Patch by: bobv, tbroyer
Review by: rchandia
Reported by: diego.dupin

Review at http://gwt-code-reviews.appspot.com/1158801


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@9309 8db76d5a-ed1c-0410-87a9-c151d255dfc7