SF 685011: calendar module overflow handling

Restored a Py2.2 behavior to not range check the day of the month.
A user application was this exploiting undocumented, accidental "feature".

Lib/calendar.py

@@ -213,7 +213,7 @@ _EPOCH_ORD = datetime.date(EPOCH, 1, 1).toordinal()
 def timegm(tuple):
     """Unrelated but handy function to calculate Unix timestamp from GMT."""
     year, month, day, hour, minute, second = tuple[:6]
-    days = datetime.date(year, month, day).toordinal() - _EPOCH_ORD
+    days = datetime.date(year, month, 1).toordinal() - _EPOCH_ORD + day - 1
     hours = days*24 + hour
     minutes = hours*60 + minute
     seconds = minutes*60 + second