This patch adds enough support for "requires unified_address" to make 
the sollve_vv testcases pass. It implements unified_address as a synonym 
of unified_shared_memory, which is both valid and the only way I know of 
to unify addresses with Cuda (could be wrong).

This patch should be applied on to of the previous patch set for USM.

OK for stage 1?

I'll apply it to OG11 shortly.

Andrew