convert BitVector to use pointer size blocks

additionally rename data-flow.* to bit-vector.* as at some point these file became very inaccurately named

BUG=
R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/683243005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25030 ce2b1a6d-e550-0410-aec6-3dcde31c8c00