calls do not introduce new bindings).

The infrastructure is already in place for fast loads from context
slots in the presence of eval.  This change simply uses that
infrastructure for calls as well as loads.

Review URL: http://codereview.chromium.org/2027002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4609 ce2b1a6d-e550-0410-aec6-3dcde31c8c00