swift234

Rename checkDefinitelyInit -> getLivenessAtUse, and split it
into two methods: one that determines the liveness of a set of
elements at a point in the CFG, and one the merges the result
across the elements used by a particular access.  The 
getLivenessAtUse is useful for traditional DI properties, but
the vector-returning one is important for analyzing the liveness
at a release.  Still no functionality change.


Swift SVN r10625