Changes GetGlobalReceiver() to GetDefaultReceiver(func) that returns undefined
for strict and native functions, and the function's context's global proxy
for "normal" functions.

BUG=v8:1547
TEST=cctest/api-test/ForeignFunctionReceiver

Review URL: http://codereview.chromium.org/7741042

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9030 ce2b1a6d-e550-0410-aec6-3dcde31c8c00