perfevent pmda

This branch contains updates to add the perfevent PMDA to the pcp dev build. It includes two tests, one runs the unit test harness and the other runs the full pmda. On RPM-based systems, the pmda is built as a separate RPM. libpfm > 4.4 is a build dependency.

I've successfully built and tested this on Ubuntu 12.04 i386, Centos 7.0 x86_64 and Centos 6.5 i386 / x86_64. Not tested on other architectures, but it should work if libpfm is available. 

Thanks,

Joe White
jpwhite4@buffalo.edu