Updated note about Linux/Alpha being stale.
Updated note about Linux/Alpha being stale.

Added note to Linux/PerfCtr section about NEVER USING PERFCTR 2.4.x
UNLESS YOU HAVE TO!

arm-hpc/papi,pyrovski/papi,pyrovski/papi,pyrovski/papi,pyrovski/papi,arm-hpc/papi,arm-hpc/papi,arm-hpc/papi,pyrovski/papi,pyrovski/papi,pyrovski/papi,arm-hpc/papi,pyrovski/papi,arm-hpc/papi,arm-hpc/papi