Adds back Util.toHexString() and Util.hex4() as deprecated methods.
They were moved to the Utility class.  This gives 3rd party linker and
generator authors a chance to migrate their code.

Review at http://gwt-code-reviews.appspot.com/1420802


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@10010 8db76d5a-ed1c-0410-87a9-c151d255dfc7