cleanup: replace False identity testing with an explicit token object

The recommended way to check default value (when None is not as option) is a
token object. Identity testing to integer is less explicit and not guaranteed to
work in all implementations.

mercurial/dirstate.py

@@ -74,6 +74,8 b' def _trypending(root, vfs, filename):'
                 raise
     return (vfs(filename), False)
 
+_token = object()
+
 class dirstate(object):
 
     def __init__(self, opener, ui, root, validate):
@@ -688,12 +690,12 b' class dirstate(object):'
         self._pl = (parent, nullid)
         self._dirty = True
 
-    def write(self, tr=False):
+    def write(self, tr=_token):
         if not self._dirty:
             return
 
         filename = self._filename
-        if tr is False: # not explicitly specified
+        if tr is _token: # not explicitly specified
             self._ui.deprecwarn('use dirstate.write with '
                                'repo.currenttransaction()',
                                '3.9')