Merged r13471, r13504 into 3.15 branch.

Correctly reset lastIndex in an RegExp object.

Fix additional spec violations wrt RegExp.lastIndex.

BUG=170856,v8:2437

R=svenpanne@chromium.org

Review URL: https://chromiumcodereview.appspot.com/12186012

git-svn-id: https://v8.googlecode.com/svn/branches/3.15@13581 ce2b1a6d-e550-0410-aec6-3dcde31c8c00