Remove Ruby 1.9 SEGV that can occur in instruction tracing a "leave" instruction.  I don't understand why we get this, calling the trace where we do in a "leave" instruction may somehow mess up cfp-> iseq such as via vm.c line 1144:
Remove Ruby 1.9 SEGV that can occur in instruction tracing a "leave"
instruction.  I don't understand why we get this, calling the trace
where we do in a "leave" instruction may somehow mess up cfp-> iseq
such as via vm.c line 1144:

  ep = ... cfp->iseq ...

Since we can handle this event via RUBY_EVENT_END I don't think
there is any loss in functionality.

rocky/rb-threadframe,rocky/rb-threadframe,rocky/rb-threadframe