[PATCH] Fix SROA creating invalid bitcasts between address spaces

[Chandler Carruth]

  After fighting some fires in SROA, all of the state for this was fresh in my head so I took another look at this.

  The patch looked essentially good at this point (and thanks for helping with the test case validation Rafael!), but pointed out some really terrible factoring and cleanup in the memcpy rewriter. I've cleaned all of that cruft up, and applied a rebased version of this patch with just a few tweaks in r202247.

http://llvm-reviews.chandlerc.com/D1764