Because there's too many options and I cannot read, I frequently get
confused between -c and -P, and try to do things like:

  perf record -P 50000 -- foo

Which does not work; try and make the option description slightly longer
and hopefully less confusing.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20150610144850.GP19282@twins.programming.kicks-ass.net
[ Do those changes on the man page as well ]
Signed-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>