the rstack functionality:
1. Fix a KASSERT that tests for the address to be above the upward
growable stack. Typically for rstack, the faulting address can be
identical to the record end of the upward growable entry, and
very likely is on ia64. The KASSERT tested for greater than, not
greater equal, so whenever the register stack had to be grown
the assertion fired.
2. When we grow the upward growable stack entry and adjust the
unlying object, don't forget to adjust the size of the VM map.
Not doing so would trigger an assert in vm_mapzdtor().
Pointy hat: marcel (for not testing with INVARIANTS).