perf list: Allow listing events with 'tracepoint' prefix

If somebody happens to name an event with the beginning of 'tracepoint'
(e.g. tracepoint_foo), then it will never be showed with perf list
event_glob, thus we parse the argument 'tracepoint' more carefully for
accuracy.

Example:

Before this patch:

 $ perf list tracepoint_foo:*

   jbd2:jbd2_start_commit                             [Tracepoint event]
   jbd2:jbd2_commit_locking                           [Tracepoint event]
   jbd2:jbd2_run_stats                                [Tracepoint event]
   block:block_rq_issue                               [Tracepoint event]
   block:block_bio_complete                           [Tracepoint event]
   block:block_bio_backmerge                          [Tracepoint event]
   block:block_getrq                                  [Tracepoint event]
   ...                                                ...

As shown above, all of the tracepoint events are printed. In fact, the
command's real intention is to print the events of tracepoint_foo.

After this patch:

 $ perf list tracepoint_foo:*

   tracepoint_foo:tp_foo_enter                        [Tracepoint event]
   tracepoint_foo:tp_foo_exit                         [Tracepoint event]

As shown above, only the events of tracepoint_foo are printed.
Signed-off-by: Yunlong Song <yunlong.song@huawei.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1425032491-20224-3-git-send-email-yunlong.song@huawei.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-list.c

@@ -50,9 +50,7 @@ int cmd_list(int argc, const char **argv, const char *prefix __maybe_unused)
 	}
 
 	for (i = 0; i < argc; ++i) {
-		if (i)
-			putchar('\n');
-		if (strncmp(argv[i], "tracepoint", 10) == 0)
+		if (strcmp(argv[i], "tracepoint") == 0)
 			print_tracepoint_events(NULL, NULL, false);
 		else if (strcmp(argv[i], "hw") == 0 ||
 			 strcmp(argv[i], "hardware") == 0)