runtime/pprof: skip test on 64-bit Mac OS X 10.6
runtime/pprof: skip test on 64-bit Mac OS X 10.6

R=rsc, bsiegert
CC=golang-dev
http://codereview.appspot.com/5709060
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go