Fix an issue where the random number generator's random event injector

Fix an issue where the random number generator's random event injector
can stall.  An interrupt could occur after rand_thread_signal is set to
0 but before the injector thread deschedules itself, resulting in the
interrupt waking up the thread before it has gone to sleep and stalling
it forever.  Also swap around the variable ordering so the SMP race
that occurs is non-harmful.  Continue to allow the race.

Reported-by: Robin Carey <robin_carey5@yahoo.co.uk>