Eliminates substantial amounts of fragile code duplication and special casing.

Also fixes "a".propertyIsEnumerable(0) to correctly return true.

R=mstarzinger@chromium.org
BUG=

Review URL: https://codereview.chromium.org/11420011

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12990 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

Fix issue 1692.

BUG=v8:1692
TEST=mjsunit/regress/regress-1692

Review URL: http://codereview.chromium.org/8113001

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9503 ce2b1a6d-e550-0410-aec6-3dcde31c8c00