Fix a starvation problem that occurs when a stream of highly interactive tasks
delay an array switch for extended periods despite EXPIRED_STARVING(rq) being
true.  AFAIKT, the only choice is to enqueue awakening tasks on the expired
array in this case.

Without this patch, it can be nearly impossible to remotely login to a busy
server, and interactive shell commands can starve for minutes.

Also, convert the EXPIRED_STARVING macro into an inline function which humans
can understand.
Signed-off-by: NMike Galbraith <efault@gmx.de>
Acked-by: NIngo Molnar <mingo@elte.hu>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Acked-by: NCon Kolivas <kernel@kolivas.org>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>