Fix for PR#6441 (Stefan Holdermans)
    
    During closure conversion, the right-hand side of a functional binding in a
    recursive binding group is now always closed as a named expression rather than
    an anonymous expression.  As a result, direct recursive calls do not need to
    retrieve their target from a closure environment.  This does not only result in
    more efficient code being generated, but also avoids a potential blocker for
    successful tail-call detection during pseudo-instruction selection.
    
    git-svn-id: http://caml.inria.fr/svn/ocaml/version/4.02@14965 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02