Added better security checks when accessing properties via Object.getOwnPropertyDescriptor.

Fixed bug in Object.defineProperty and related access bugs (issues 992, 1083 and 1092).

Added LICENSE.v8, LICENSE.strongtalk and LICENSE.valgrind to ease copyright notice generation for embedders.


git-svn-id: https://v8.googlecode.com/svn/trunk@6662 ce2b1a6d-e550-0410-aec6-3dcde31c8c00