rcu: fixes to include/linux/rcupreempt.h

Hello!

Compared tip/core/rcu to my latest patchset, and found the following
issues:

o	the memory barrier in rcu_exit_nohz() somehow got out of place
	(it is correct in mainline as of 2.6.26-rc7).

o	There is a duplicate declaration of rcu_dyntick_sched.

The attached patch fixes these.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>