Fix bug in edge case in populating PointerMaps

Fix bug in edge case in populating PointerMaps

If a live range was split immediately before an instruction that required a
safe-point pointer map, it was possible for the safe-point to incorrectly use the
register/stack slot information of the preceeding live range rather than the one
that actually covers the safe-point.

R=mstarzinger@chromium.org,vegorov@chromium.org

Review URL: https://chromiumcodereview.appspot.com/12040052

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@13493 ce2b1a6d-e550-0410-aec6-3dcde31c8c00