Allow evals for debugger even if they are prohibited in the debugee context. (Chromium issue 154733)

Enabled --verify-heap in release mode (issue 2120)

Performance and stability improvements on all platforms.

git-svn-id: http://v8.googlecode.com/svn/trunk@12729 ce2b1a6d-e550-0410-aec6-3dcde31c8c00