The panic results from skewed mapping upon excessive cowfaults. 

Changing memory protection under certain conditions can result 
in a "kernel memory fault" panic

This patch fixes cases where some state in multithreaded tasks 
was not properly being cleaned up.




 0 boot
 1 panic
 2 vm_pg_free
 3 u_anon_free
 4 u_anon_unmap
 5 u_map_delete
 6 vm_map_exit
 7 exit
 8 syscall
 9 _Xsyscall

 0 panic
 1 event_timeout
 2 printf
 3 panic
 4 trap
 5 _XentMM
 6 _a_lock
 7 u_anon_protect
 8 u_map_protect
 9 mprotect 
10 syscall 
11 _Xsyscall


