Add "Z" as an alias for the timezone "UTC"

The name "Z" for the UTC timezone is required to properly parse ISO 8601
timestamps.  Add it to the list of recognized timezones.

Because timezone names can be shorter than 3 letters, loosen the
restriction in match_alpha() that used to require at least 3 letters to
match to allow a short timezone name as long as it matches exactly.  Prior
to the introduction of the "Z" zone, this already affected the timezone
"NT" (Nome).

Signed-off-by: Marcus Comstedt <marcus@mc.pp.se>
Reviewed-by: Jay Soffian <jaysoffian@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

date.c

@@ -229,6 +229,7 @@ static const struct {
 
 	{ "GMT",    0, 0, },	/* Greenwich Mean */
 	{ "UTC",    0, 0, },	/* Universal (Coordinated) */
+	{ "Z",      0, 0, },    /* Zulu, alias for UTC */
 
 	{ "WET",    0, 0, },	/* Western European */
 	{ "BST",    0, 1, },	/* British Summer */
@@ -305,7 +306,7 @@ static int match_alpha(const char *date, struct tm *tm, int *offset)
 
 	for (i = 0; i < ARRAY_SIZE(timezone_names); i++) {
 		int match = match_string(date, timezone_names[i].name);
-		if (match >= 3) {
+		if (match >= 3 || match == strlen(timezone_names[i].name)) {
 			int off = timezone_names[i].offset;
 
 			/* This is bogus, but we like summer */