util: add an optional timestamp parameter to makedate

This will be used by the upcoming shelve extension.

mercurial/util.py

@@ -997,9 +997,10 b' def filechunkiter(f, size=65536, limit=N'
             limit -= len(s)
         yield s
 
-def makedate():
-    '''Return the current time as a (unixtime, offset) tuple based off
-    the local timezone.'''
+def makedate(timestamp=None):
+    '''Return a unix timestamp (or the current time) as a (unixtime,
+    offset) tuple based off the local timezone.'''
+    if timestamp is None:
     timestamp = time.time()
     if timestamp < 0:
         hint = _("check your clock")