This fixes updating of property attributes for getters and setters on
dictionary elements while redefining. This just updates the property
details on the existing element.

R=rossberg@chromium.org
BUG=v8:1772
TEST=test262

Review URL: http://codereview.chromium.org/8337013

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9685 ce2b1a6d-e550-0410-aec6-3dcde31c8c00