Fixes so apichecker works on Windows, by making the refJar path an ant "path" <arg> and splitting
on path.separator, not ":".  Also, arg parsing is changed to return an error status, so typos and
such stop the builds.

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@5721 8db76d5a-ed1c-0410-87a9-c151d255dfc7