revset: added isascending and isdescending methods to _addset

This methods are intended to duck-type baseset, so we will still have _addset
as a private class but now we can return it without wrapping it into an
orderedlazyset or a lazyset.

These were the last methods to add for smartset compatibility.

mercurial/revset.py

@@ -2519,6 +2519,12 @@ class _addset(object):
             if bool(self._ascending) == bool(reverse):
                 self.reverse()
 
+    def isascending(self):
+        return self._ascending is not None and self._ascending
+
+    def isdescending(self):
+        return self._ascending is not None and not self._ascending
+
     def reverse(self):
         self._list.reverse()
         if self._ascending is not None: