Avoid excessive memory usage during redundant phi elimination. (issue 2510)

Fixed additional spec violations wrt RegExp.lastIndex. (issue 2437)

Added Isolate parameter to Persistent class. (issue 2487)

Performance and stability improvements on all platforms.

git-svn-id: http://v8.googlecode.com/svn/trunk@13508 ce2b1a6d-e550-0410-aec6-3dcde31c8c00