changing the install location of hal-system-power-pmu to libexec

[Artem Kachitchkine]

> Just renaming it isn't an option unless it also moves out of /usr/share 
> - compiled C code has to go under /usr/lib (or libexec).

Keeping stuff under /usr/lib/hal might not be such a bad idea as to warrant code 
rewrite. I don't know what filesystem hierarchy standards say about that, but 
it's a pretty standard practice in Solaris.

-Artem.