Use RFC2822 dates from "git fmt-patch".

Still Work-in-progress git fmt-patch (should it be known as
format-patch-ng?) is matched with the fix made by Huw Davies
in 262a6ef7 commit to use
RFC2822 date format.
Signed-off-by: NJunio C Hamano <junkio@cox.net>

cache.h

@@ -249,6 +249,7 @@ extern void *read_object_with_reference(const unsigned char *sha1,
 					unsigned char *sha1_ret);
 
 const char *show_date(unsigned long time, int timezone);
+const char *show_rfc2822_date(unsigned long time, int timezone);
 int parse_date(const char *date, char *buf, int bufsize);
 void datestamp(char *buf, int bufsize);
 unsigned long approxidate(const char *);

commit.c

@@ -442,7 +442,8 @@ static int add_user_info(const char *what, enum cmit_fmt fmt, char *buf, const c
 		ret += sprintf(buf + ret, "Date:   %s\n", show_date(time, tz));
 		break;
 	case CMIT_FMT_EMAIL:
-		ret += sprintf(buf + ret, "Date: %s\n", show_date(time, tz));
+		ret += sprintf(buf + ret, "Date: %s\n",
+			       show_rfc2822_date(time, tz));
 		break;
 	case CMIT_FMT_FULLER:
 		ret += sprintf(buf + ret, "%sDate: %s\n", what, show_date(time, tz));

date.c

@@ -42,18 +42,24 @@ static const char *weekday_names[] = {
  * thing, which means that tz -0100 is passed in as the integer -100,
  * even though it means "sixty minutes off"
  */
-const char *show_date(unsigned long time, int tz)
+static struct tm *time_to_tm(unsigned long time, int tz)
 {
-	struct tm *tm;
 	time_t t;
-	static char timebuf[200];
 	int minutes;
 
 	minutes = tz < 0 ? -tz : tz;
 	minutes = (minutes / 100)*60 + (minutes % 100);
 	minutes = tz < 0 ? -minutes : minutes;
 	t = time + minutes * 60;
-	tm = gmtime(&t);
+	return gmtime(&t);
+}
+
+const char *show_date(unsigned long time, int tz)
+{
+	struct tm *tm;
+	static char timebuf[200];
+
+	tm = time_to_tm(time, tz);
 	if (!tm)
 		return NULL;
 	sprintf(timebuf, "%.3s %.3s %d %02d:%02d:%02d %d %+05d",
@@ -65,6 +71,21 @@ const char *show_date(unsigned long time, int tz)
 	return timebuf;
 }
 
+const char *show_rfc2822_date(unsigned long time, int tz)
+{
+	struct tm *tm;
+	static char timebuf[200];
+
+	tm = time_to_tm(time, tz);
+	if (!tm)
+		return NULL;
+	sprintf(timebuf, "%.3s, %d %.3s %d %02d:%02d:%02d %+05d",
+		weekday_names[tm->tm_wday], tm->tm_mday,
+		month_names[tm->tm_mon], tm->tm_year + 1900,
+		tm->tm_hour, tm->tm_min, tm->tm_sec, tz);
+	return timebuf;
+}
+
 /*
  * Check these. And note how it doesn't do the summer-time conversion.
  *