Adds 3 new completion API calls, which are a straightforward extension of
the current APIs:

 int wait_for_completion_interruptible(struct completion *x);
 unsigned long wait_for_completion_timeout(struct completion *x,
                                                   unsigned long timeout);
 unsigned long wait_for_completion_interruptible_timeout(
                        struct completion *x, unsigned long timeout);

This enables the conversion of more semaphore-using code to completions.
There is code that cannot be converted right now (and is forced to use
semaphores) because these primitives are missing.  Thomas Gleixner has a
bunch of patches to make use of them.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Tested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>