Merge UpdateStoreCaches into a single function dispatching on ComputeStoreMonorphic and UpdateMegamorphicCache.

Review URL: https://chromiumcodereview.appspot.com/12057003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13503 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Fix additional spec violations wrt RegExp.lastIndex.

R=svenpanne@chromium.org
BUG=v8:2437

Review URL: https://chromiumcodereview.appspot.com/12033099

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13504 ce2b1a6d-e550-0410-aec6-3dcde31c8c00