diff-merges: adapt -m to enable default diff format

Let -m option (and --diff-merges=m) enable the default format instead
of "separate", to be able to tune it with log.diffMerges option.

Signed-off-by: Sergey Organov <sorganov@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff-merges.c

@@ -34,10 +34,10 @@ static void set_m(struct rev_info *revs)
 {
 	/*
 	 * To "diff-index", "-m" means "match missing", and to the "log"
-	 * family of commands, it means "show full diff for merges". Set
+	 * family of commands, it means "show default diff for merges". Set
 	 * both fields appropriately.
 	 */
-	set_separate(revs);
+	set_to_default(revs);
 	revs->match_missing = 1;
 }
 
@@ -61,13 +61,13 @@ static diff_merges_setup_func_t func_by_opt(const char *optarg)
 		return suppress;
 	if (!strcmp(optarg, "1") || !strcmp(optarg, "first-parent"))
 		return set_first_parent;
-	else if (!strcmp(optarg, "m") || !strcmp(optarg, "separate"))
+	else if (!strcmp(optarg, "separate"))
 		return set_separate;
 	else if (!strcmp(optarg, "c") || !strcmp(optarg, "combined"))
 		return set_combined;
 	else if (!strcmp(optarg, "cc") || !strcmp(optarg, "dense-combined"))
 		return set_dense_combined;
-	else if (!strcmp(optarg, "on"))
+	else if (!strcmp(optarg, "m") || !strcmp(optarg, "on"))
 		return set_to_default;
 	return NULL;
 }