kernel - Correct second edge-case for machdep.pmap_mmu_optimize

kernel - Correct second edge-case for machdep.pmap_mmu_optimize

* The pmap_release*() code was previously optimized to not invalidate
  on pml4, pdp, pd, or pt pte's, only on terminal ptes.  This invalidation
  interferes with the PT replacement that the pmap_mmu_optimize feature
  uses.

* The bug generally would only occur when memory is mmap()'d and munmap()'d
  multiple times, which something like postgres will not do, but which
  rtorrent and other programs will do.

* Correctly invalidate page tables (use invltlb) when PT pte's are replaced.

* Requires further testing.  Default for this feature is still off.