There was an unnecessary load on every statically-resolved context lookup.
Remove it.

This revealed a hidden bug in const initializers inside 'with'.  They claim
to be statically resolved (having slot type CONTEXT) but they occur in a
spot where the runtime context chain and the static scope chain do not
agree.  This is fixed by special casing const initializers in the backend.

Review URL: http://codereview.chromium.org/6384020

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6635 ce2b1a6d-e550-0410-aec6-3dcde31c8c00