THis patch invalidates a range-op handler object if an operand type in 
the statement is not supported.

This also triggered a check in stmt dependency resolution which assumed 
there must be a valid handler for any stmt with an appropriate LHS 
type... which is a false assumption.

This should do for now, but long term I will rework the dispatch code to 
ensure it matches the specifically supported patterns of operands. This 
will make the handler creation a little slower, but speed up the actual 
dispatch, especially as we add new range types next release.  Its also 
much more invasive... too much for this release I think.

bootstraps on x86_64-pc-linux-gnu with no regressions.  OK?

Andrew