abstractsmartset: default implementation for `ascending` and `descending`

These two methods are actually silly aliases for `sort()` and
`sort(reverse=True)`. So we get that aliasing at the abstractsmartset level. We
will slowly phase out all the custom implementations and eventually remove any
mentions of it from the code.

mercurial/revset.py

@@ -2226,7 +2226,7 b' class abstractsmartset(object):'
         """Sorts the set in ascending order (in place).
 
         This is part of the mandatory API for smartset."""
-        raise NotImplementedError()
+        self.sort()
 
     def isdescending(self):
         """True if the set will iterate in descending order"""
@@ -2236,7 +2236,7 b' class abstractsmartset(object):'
         """Sorts the set in descending order (in place).
 
         This is part of the mandatory API for smartset."""
-        raise NotImplementedError()
+        self.sort(reverse=True)
 
     def min(self):
         """return the minimum element in the set"""