Handled return-value of SetElement in some cases, or avoided it in other.

Handled return-value of SetElement in some cases, or avoided it in other.

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