[PATCH] [Reassocate] Add support for vector instructions.

[hfinkel at anl.gov]

Two further comments:

 1. Once you have the rebased patch, please post it with full context (http://llvm.org/docs/Phabricator.html)

 2. We should split the test cases so the primary tests depend only on the reassociate pass. However, you can also add tests to instcombine/GVN/etc. so that we make sure the end-to-end result has coverage.

http://reviews.llvm.org/D5222