probe hrtimer testing

[Roland McGrath]

Just to reiterate, itimer.c (and posix-timers.c) implement the user syscall
ABIs for timers, and the only things they can be used for are affecting the
user-visible ABI components.  Those are implemented in terms of the
kernel's internal timer facilities.  Anything in private kernel code such
as systemtap probes/runtime must be done using those facilities, and they
are easy to use for it.  In the latest kernels, the hrtimer interface is
the preferred internal timer facility and is now the canonical thing to use
in new kernel code (regardless of what granularity you are going to ask for).