exit() almost there.

- Implemented reasonable way to suspend task.
  - A task that has a pending suspend would be interrupted
    from its sleep via the suspender task.
  - If suspend was raised and right after, task became about to sleep,
    then scheduler wakes it up.
  - If suspend was raised when task was in user mode, then an irq suspends it.
  - Also suspends are checked at the end of a syscall so that if suspend was
    raised because of a syscall from the task, the task is suspended before it
    goes back to user mode.

  - This mechanism is very similar to signals, and it may lead as a base for
    implementing signal handling.

- Implemented common vma dropping for shadow vm object dropping and task exiting.

include/l4/lib/wait.h

@@ -10,6 +10,11 @@ struct waitqueue {
 	struct ktcb *task;
 };
 
+enum wakeup_flags {
+	WAKEUP_INTERRUPT = (1 << 0),
+	WAKEUP_SYNC	 = (1 << 1)
+};
+
 #define CREATE_WAITQUEUE_ON_STACK(wq, tsk)		\
 struct waitqueue wq = {					\
 	.task_list = { &wq.task_list, &wq.task_list },	\
@@ -65,9 +70,9 @@ do {								\
 	}							\
 } while(0);
 
-void wake_up(struct waitqueue_head *wqh, int sync);
-int wake_up_task(struct ktcb *task, int sync);
-void wake_up_all(struct waitqueue_head *wqh, int sync);
+void wake_up(struct waitqueue_head *wqh, unsigned int flags);
+int wake_up_task(struct ktcb *task, unsigned int flags);
+void wake_up_all(struct waitqueue_head *wqh, unsigned int flags);
 
 #endif /* __LIB_WAIT_H__ */