Port r10220 (1dae466).

Original commit message:

This CL adds support for loading from and storing to context slots
belonging to harmony let or const bound variables. Checks for the
hole value are performed and the function is deoptimized if they fail.
The full-codegen generated code will take care of properly throwing
a reference error in these cases.

BUG=
TEST=

Review URL: http://codereview.chromium.org/8897025
Patch from Daniel Kalmar <kalmard@homejinni.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10235 ce2b1a6d-e550-0410-aec6-3dcde31c8c00