Perfcounters added to the mainline

there is hope that soon PAPI and pfmon (the perfmon2 tool) will be ported to perfcounters, so assuming the features they need are available, things might work out in the end once things stabilize for a few months/years.

It will be nice that _finally_ performance counters will be available under Linux without having to patch the kernel. It's just a shame that it happened the way it did.