This change fixes the deoptimization when a keyed load is used with
a symbol key. Before we would wrongly generate a fast elements load.
Now we generate a generic keyed load instead.

BUG=1471
Review URL: http://codereview.chromium.org/7150010

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8281 ce2b1a6d-e550-0410-aec6-3dcde31c8c00