perf/scripts: Fix supported language listing option

'perf trace -s list' prints a list of the supported scripting
languages.  One problem with it is that it falls through and prints
the trace as well.  The use of 'list' for this also makes it easy to
confuse with 'perf trace -l', used for listing available scripts.  So
change 'perf trace -s list' to 'perf trace -s lang' and fixes the
fall-through problem.
Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Keiichi KII <k-keiichi@bx.jp.nec.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <1264580883-15324-2-git-send-email-tzanussi@gmail.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

tools/perf/Documentation/perf-trace.txt

@@ -45,9 +45,11 @@ OPTIONS
 --list=::
         Display a list of available trace scripts.
 
--s::
+-s ['lang']::
 --script=::
         Process trace data with the given script ([lang]:script[.ext]).
+	If the string 'lang' is specified in place of a script name, a
+        list of supported languages will be displayed instead.
 
 -g::
 --gen-script=::

tools/perf/builtin-trace.c

@@ -219,9 +219,9 @@ static int parse_scriptname(const struct option *opt __used,
 	const char *script, *ext;
 	int len;
 
-	if (strcmp(str, "list") == 0) {
+	if (strcmp(str, "lang") == 0) {
 		list_available_languages();
-		return 0;
+		exit(0);
 	}
 
 	script = strchr(str, ':');