Switching to new GASNet version

Having heard no objections, I'm changing over to the new version of
GASNet to see how it does in nightly testing and whether we're ready
to make it the default.



git-svn-id: http://svn.code.sf.net/p/chapel/code/trunk@22160 3a8e244f-b0f2-452b-bcba-4c88e055c3ca