Do not try to unmark MAP_ENTRY_IN_TRANSITION marked by other thread.

Do not try to unmark MAP_ENTRY_IN_TRANSITION marked by other thread.

The issue is catched by "vm_map_wire: alien wire" KASSERT at the end
of the vm_map_wire().  We currently check for MAP_ENTRY_WIRE_SKIPPED
flag before ensuring that the wiring_thread is curthread. For HOLESOK
wiring, this means that we might see WIRE_SKIPPED entry from different
wiring.

The fix it by only checking WIRE_SKIPPED if the entry is put
IN_TRANSITION by us.  Also fixed a typo in the comment explaining the
situation.

Reported and tested by:	pho
Reviewed by:	alc
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week