perf tools: Accept case-insensitive symbolic event variants

We currently fail on something like '-e CPU-migrations', with:

  invalid or unsupported event: 'CPU-migrations'

While 'CPU-migrations' is how we actually print out the event
in the default perf stat output:

 Performance counter stats for 'true':

          0.202204 task-clock-msecs         #      0.282 CPUs
                 0 context-switches         #      0.000 M/sec
                 0 CPU-migrations           #      0.000 M/sec

So change the matching to be case-insensitive.
Acked-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: NArnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Link: http://lkml.kernel.org/n/tip-omcm3edjjtx83a4kh2e244se@git.kernel.orgSigned-off-by: NIngo Molnar <mingo@elte.hu>

tools/perf/util/parse-events.c

@@ -649,13 +649,15 @@ static int check_events(const char *str, unsigned int i)
 	int n;
 
 	n = strlen(event_symbols[i].symbol);
-	if (!strncmp(str, event_symbols[i].symbol, n))
+	if (!strncasecmp(str, event_symbols[i].symbol, n))
 		return n;
 
 	n = strlen(event_symbols[i].alias);
-	if (n)
-		if (!strncmp(str, event_symbols[i].alias, n))
+	if (n) {
+		if (!strncasecmp(str, event_symbols[i].alias, n))
 			return n;
+	}
+
 	return 0;
 }