perf tools: Setup pager when printing usage and help

It's annoying to see error or help message when command has many options
like in perf record, report or top. So setup pager when print parser
error or help message - it should be OK since no UI is enabled at the
parsing time. The usage_with_options() already disables it by calling
exit_browser() anyway.

Signed-off-by: Namhyung Kim <[e-mail]>
Acked-by: Ingo Molnar <[e-mail]>
Tested-by: Arnaldo Carvalho de Melo <[e-mail]>
Cc: David Ahern <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/parse-options.c

···
 #define OPT_SHORT 1
 #define OPT_UNSET 2
 
+static struct strbuf error_buf = STRBUF_INIT;
+
 static int opterror(const struct option *opt, const char *reason, int flags)
 {
 	if (flags & OPT_SHORT)
···
 		exit(130);
 	default: /* PARSE_OPT_UNKNOWN */
 		if (ctx.argv[0][1] == '-') {
-			error("unknown option `%s'", ctx.argv[0] + 2);
+			strbuf_addf(&error_buf, "unknown option `%s'",
+				    ctx.argv[0] + 2);
 		} else {
-			error("unknown switch `%c'", *ctx.opt);
+			strbuf_addf(&error_buf, "unknown switch `%c'",
+				    *ctx.opt);
 		}
 		usage_with_options(usagestr, options);
 	}
···
 
 	if (!usagestr)
 		return PARSE_OPT_HELP;
+
+	setup_pager();
+
+	if (strbuf_avail(&error_buf)) {
+		fprintf(stderr, "  Error: %s\n", error_buf.buf);
+		strbuf_release(&error_buf);
+	}
 
 	fprintf(stderr, "\n Usage: %s\n", *usagestr++);
 	while (*usagestr && **usagestr)