Implement process CPU percent usage about psutil HOT 7 CLOSED

Implemented for Windows as r230 , for FreeBSD as r238 and for OS X as r239 .
On Linux it was already implemented as r225 .
Leaving this open as long as we figure out if we can set up a minimal test case at least.

Issue 35 's get_num_cpus() is now implemented on all platform.
Assigning this to Jay to modify get_cpu_percent() to work on multiple cores.

Actually you can do this if you want, all we have to do is make sure the percentage
is divided by # of CPUs to provide an "overall" CPU % value as a float.

Fixed as r248 .

Updated csets after the SVN -> Mercurial migration: r225 == revision e7ec84bc5f8e r230 == revision 96957c8b5214 r248 == revision 7ce5924fc7ad