Adding explicit casts to the return value of certain methods to help the javac compiler.  Some compilers require the explicit cast.

Review at http://gwt-code-reviews.appspot.com/1463810

Review by: robertvawter@google.com

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@10413 8db76d5a-ed1c-0410-87a9-c151d255dfc7