In List::Add, correctly handle the case of adding a reference to a

In List::Add, correctly handle the case of adding a reference to a
preexisting list element to a list, and to not return anything (we
never used the return value).  Remove List::Insert, it is not
currently used or needed.  Change List::AddBlock to take a copy of
the element to be replicated rather than a reference.

Review URL: http://codereview.chromium.org/39148

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1424 ce2b1a6d-e550-0410-aec6-3dcde31c8c00