perf record: Print out the number of events captured

It makes sense to inform the user about how many events
perf record has written - so that the sufficiency of
profiling coverage and intensity can be determined at
a glance.

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Kacur <jkacur@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

Documentation/perf_counter/builtin-record.c

@@ -467,6 +467,9 @@ static int __cmd_record(int argc, const char **argv)
 			ret = poll(event_array, nr_poll, 100);
 	}
 
+
+	fprintf(stderr, "[ perf record: Captured and wrote %ld events. ]\n", events);
+
 	return 0;
 }