- Create an unmapped guard page to trap access to vm_page_array[-1].

This guard page would have trapped the problems with the MFC of the PAE
   support to RELENG_4 at an earlier point in the sequence of events.

Submitted by:	tegge

sys/vm/vm_page.c

@@ -241,6 +241,11 @@ vm_page_startup(vm_offset_t starta, vm_offset_t enda, vm_offset_t vaddr)
 	    (end - new_end)) / PAGE_SIZE;
 	end = new_end;
 
+	/*
+	 * Reserve an unmapped guard page to trap access to vm_page_array[-1].
+	 */
+	vaddr += PAGE_SIZE;
+
 	/*
 	 * Initialize the mem entry structures now, and put them in the free
 	 * queue.