[PATCH] ia64: Fix OSDL BugMe report 2885: realtime process can't preempt low priority process in kernel

Rearranged code to make it work. There were two problems:

 1. The preempt flag was being tested only if code was leaving for
    user space (the logic should be: test for RESCHEDULE if we're
    switching to a kernel thread, test everything if switching to a
    user thread)

 2. The check of the user space flags was being repeated even if the
    work had been done.

There is one small change in semantics: when returning from a
preemption, the preemption flag will *not* be rechecked.  Otherwise, I
found that it was easy to get into a livelock situation where no
forward progress was made.
Signed-off-by: David Mosberger <davidm@hpl.hp.com>