Managed to self-destruct pager.

Issues:
- A page-faulting thread suspends if receives -1 from pager page fault ipc.
  This is fine if pager is about to delete the thread, but it is not if
  it is a buggy pager.
- Need to find a way to completely get rid of suspended pager.
- A method of deleting suspended tasks could remedy both cases above.

include/l4/generic/tcb.h

@@ -28,6 +28,7 @@
 #define TASK_INTERRUPTED		(1 << 0)
 #define TASK_SUSPENDING			(1 << 1)
 #define TASK_RESUMING			(1 << 2)
+#define TASK_EXITING			(1 << 3)
 
 /* Task states */
 enum task_state {