VM wiring fixed

[Don Lewis]

On 28 Apr, Brian Fundakowski Feldman wrote:

> * vm_map_{un,}wire() did not keep track of wirings as they should.  User
>   wirings are separate from system wirings, and there can be exactly one.
>   There can be unlimited system wirings, but wired_count will remain at
>   zero for map entries that are allocated as MAP_ENTRY_NOFAULT.

This is something that I started to worry about when I was making my
mlock()/vslock() changes a while back.  I was hoping to find time to
mention my concerns, but I never accumulated enough round tuits.  I'm
really glad to see attention paid to this issue.