Added the ability for an embedding application to receive a callback when V8 allocates (V8::AddMemoryAllocationCallback) or deallocates (V8::RemoveMemoryAllocationCallback) from the OS.

Fixed several JSON bugs (including issue 855).

Fixed memory overrun crash bug triggered during V8's tick-based profiling.

Performance improvements on all platforms.

git-svn-id: http://v8.googlecode.com/svn/trunk@5412 ce2b1a6d-e550-0410-aec6-3dcde31c8c00