In the presence of JS accessors for elements on Object.prototype JSArray::SetFastElement
may throw or its behaviour can be altered.  Instead operate on plain FixedArrays and
turn them into JSArry later.

BUG=v8:1130
TEST=test/mjsunit/regress/regress-1130.js

Review URL: http://codereview.chromium.org/6481001

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6730 ce2b1a6d-e550-0410-aec6-3dcde31c8c00