for-each-ref: "creator" and "creatordate" fields

This adds "creator" (which is parallel to "tagger" or "committer")
and "creatordate" (corresponds to "taggerdate" and
"committerdate").

As other "date" fields, "creatordate" sorts numerically
and displays human readably. This allows for example for
sorting together heavyweigth and lightweight tags.
Signed-off-by: NJunio C Hamano <junkio@cox.net>
Acked-by: NJakub Narebski <jnareb@gmail.com>

builtin-for-each-ref.c

@@ -59,6 +59,8 @@ static struct {
 	{ "taggername" },
 	{ "taggeremail" },
 	{ "taggerdate", FIELD_TIME },
+	{ "creator" },
+	{ "creatordate", FIELD_TIME },
 	{ "subject" },
 	{ "body" },
 	{ "contents" },
@@ -401,6 +403,29 @@ static void grab_person(const char *who, struct atom_value *val, int deref, stru
 		else if (!strcmp(name + wholen, "date"))
 			grab_date(wholine, v);
 	}
+
+	/* For a tag or a commit object, if "creator" or "creatordate" is
+	 * requested, do something special.
+	 */
+	if (strcmp(who, "tagger") && strcmp(who, "committer"))
+		return; /* "author" for commit object is not wanted */
+	if (!wholine)
+		wholine = find_wholine(who, wholen, buf, sz);
+	if (!wholine)
+		return;
+	for (i = 0; i < used_atom_cnt; i++) {
+		const char *name = used_atom[i];
+		struct atom_value *v = &val[i];
+		if (!!deref != (*name == '*'))
+			continue;
+		if (deref)
+			name++;
+
+		if (!strcmp(name, "creatordate"))
+			grab_date(wholine, v);
+		else if (!strcmp(name, "creator"))
+			v->s = copy_line(wholine);
+	}
 }
 
 static void find_subpos(const char *buf, unsigned long sz, const char **sub, const char **body)