new patch for "Previous IPI is stuck" - PLEASE TEST

Hi,

The last patch for Previous IPI is stuck" seems to have fixed the
problem for all testers (Thanks for the feedback!) and this is the
promised optimized version.

You can download the patch at:
	http://people.freebsd.org/~ups/ipi5_patch
	Please make sure that exception.o is rebuild.
	( Makefile seems to miss the dependency to apic_vector.s) 

I would like to check in the changes as soon as possible.
However since I can not reproduce the problem locally I will have to
wait for feedback from testers.
Thanks again to all for the positive feedback for the last patch.

	Stephan