Release stack trace data after firing Error.stack accessor. (issue 2308)

Added a new API V8::SetJitCodeEventHandler to push code name and location to users such as profilers.

Allocate block-scoped global bindings to global context.

Performance and stability improvements on all platforms.

git-svn-id: http://v8.googlecode.com/svn/trunk@12408 ce2b1a6d-e550-0410-aec6-3dcde31c8c00