Lastest kprobes64 patch

[David Long]

In repsonse to the prolonged discussion on issues with use of a 
duplicated stack for jprobes on arm64 I have created the requested 
change of removing the stack duplication code altogether.  I don't know 
how this affects systemtap.  It would also be good to have a better idea 
of how much systemtap makes use of jprobes.

The new additional patch, plus Catalin's accumulated patches since 
kprobes64-v15, are now in my (recreated) kprobes64-v16 branch.  If 
someone has time to exercise this it I would be grateful.

Thanks,
-dl