t/helper: merge test-revision-walking into test-tool

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/helper/test-revision-walking.c

@@ -8,6 +8,7 @@
  * published by the Free Software Foundation.
  */
 
+#include "test-tool.h"
 #include "cache.h"
 #include "commit.h"
 #include "diff.h"
@@ -45,7 +46,7 @@ static int run_revision_walk(void)
 	return got_revision;
 }
 
-int cmd_main(int argc, const char **argv)
+int cmd__revision_walking(int argc, const char **argv)
 {
 	if (argc < 2)
 		return 1;