Add a compiler flag -XdisableRunAsync to disable code-splitting on a per-compile basis.
Mainly intended for tech-demonstration and diagnostic purposes.

Patch by: bobv
Review by: spoon


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@4346 8db76d5a-ed1c-0410-87a9-c151d255dfc7