kernel - VM rework part 13 - Core pmap work, stabilize & optimize

kernel - VM rework part 13 - Core pmap work, stabilize & optimize

* Refactor the vm_page_hash hash again to get a better distribution.

* I tried to only hash shared objects but this resulted in a number of
  edge cases where program re-use could miss the optimization.

* Add a sysctl vm.page_hash_vnode_only (default off).  If turned on,
  only vm_page's associated with vnodes will be hashed.  This should
  generally not be necessary.

* Refactor vm_page_list_find2() again to avoid all duplicate queue
  checks.  This time I mocked the algorithm up in userland and twisted
  it until it did what I wanted.

* VM_FAULT_QUICK_DEBUG was accidently left on, turn it off.

* Do not remove the original page from the pmap when vm_fault_object()
  must do a COW.  And just in case this is ever added back in later,
  don't do it using pmap_remove_specific() !!!  Use pmap_remove_pages()
  to avoid the backing scan lock.

  vm_fault_page() will now do this removal (for procfs rwmem), the normal
  vm_fault will of course replace the page anyway, and the umtx code
  uses different recovery mechanisms now and should be ok.

* Optimize vm_map_entry_shadow() for the situation where the old
  object is no longer shared.  Get rid of an unnecessary transient
  kmalloc() and vm_object_hold_shared().