date.c: add "show_date()" function.

Kind of like ctime(), but not as broken.

cache.h

@@ -166,6 +166,7 @@ extern void *read_object_with_reference(const unsigned char *sha1,
 					unsigned long *size,
 					unsigned char *sha1_ret);
 
+const char *show_date(unsigned long time, int timezone);
 void parse_date(char *date, char *buf, int bufsize);
 void datestamp(char *buf, int bufsize);
 

date.c

@@ -38,6 +38,34 @@ static const char *weekday_names[] = {
 	"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"
 };
 
+/*
+ * The "tz" thing is passed in as this strange "decimal parse of tz"
+ * 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)
+{
+	struct tm *tm;
+	time_t t;
+	static char timebuf[200];
+	int minutes;
+
+	minutes = tz < 0 ? -tz : tz;
+	minutes = (tz / 100)*60 + (tz % 100);
+	minutes = tz < 0 ? -minutes : minutes;
+	t = time - minutes * 60;
+	tm = gmtime(&t);
+	if (!tm)
+		return NULL;
+	sprintf(timebuf, "%.3s %.3s %d %02d:%02d:%02d %d %+05d",
+		weekday_names[tm->tm_wday],
+		month_names[tm->tm_mon],
+		tm->tm_mday,
+		tm->tm_hour, tm->tm_min, tm->tm_sec,
+		tm->tm_year + 1900, tz);
+	return timebuf;
+}
+
 /*
  * Check these. And note how it doesn't do the summer-time conversion.
  *