better handle errors with date parsing (issue983)

Windows cannot always handle a 1970-01-01 parameter to time.mktime().

mercurial/util.py

@@ -1541,7 +1541,7 b' def parsedate(string, formats=None, defa'
         for format in formats:
             try:
                 when, offset = strdate(string, format, defaults)
-            except ValueError:
+            except (ValueError, OverflowError):
                 pass
             else:
                 break