instead of normal JSObjects.

This ensures that __proto__ and accessors on the Object prototype do
not interfere with catch scopes.  Also, it fixes the bug that catch
variables were not DontDelete (issue 74).

Next step is to create special lookup routines for context extension
objects and remove the special handling of context extension objects
from the general javascript object lookup routines.
Review URL: http://codereview.chromium.org/18143

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1091 ce2b1a6d-e550-0410-aec6-3dcde31c8c00