perf script: look up thread using tid instead of pid

This allows the thread name to be dispalyed when dumping
events:
           myapp 25118 [000] 450385.538815: context-switches ...
    myapp:worker 25119 [000] 450385.538894: context-switches ...

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1324578603-12762-4-git-send-email-dsahern@gmail.com
Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-script.c

@@ -443,7 +443,7 @@ static int process_sample_event(struct perf_tool *tool __used,
 				struct machine *machine)
 {
 	struct addr_location al;
-	struct thread *thread = machine__findnew_thread(machine, event->ip.pid);
+	struct thread *thread = machine__findnew_thread(machine, event->ip.tid);
 
 	if (thread == NULL) {
 		pr_debug("problem processing %d event, skipping it.\n",