py3: convert date and format arguments str before passing in time.strptime

time.strptime() raises ValueError if the arguments are not str.
Source Code: https://hg.python.org/cpython/file/3.5/Lib/_strptime.py#l307

mercurial/util.py

@@ -1937,7 +1937,8 b' def strdate(string, format, defaults=Non'
             # elements are relative to today
             usenow = True
 
-    timetuple = time.strptime(date, format)
+    timetuple = time.strptime(encoding.strfromlocal(date),
+                              encoding.strfromlocal(format))
     localunixtime = int(calendar.timegm(timetuple))
     if offset is None:
         # local timezone