SetElement can cause an exception to be thrown. If its return value
isn't checked, this exception might not be handled at the correct time.
In some cases, it's a matter of returning Exception::Failure() from
a runtime function.
In other cases, code using SetElement on a JSArray has been changed
to setting directly on a FixedArray and only creating the JSArray
at the end.

Review URL: http://codereview.chromium.org/6588130

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7039 ce2b1a6d-e550-0410-aec6-3dcde31c8c00