Version 3.20.0

Migrated several tests from blink to V8 repository.

Allowed users of the V8 API to distinguish between unset and undefined HiddenValues (issue 2746).

Deprecated old style callbacks in the V8 API.

Turned on parallel recompilation.

Performance and stability improvements on all platforms.

git-svn-id: https://v8.googlecode.com/svn/trunk@15386 ce2b1a6d-e550-0410-aec6-3dcde31c8c00