revset: made ascgeneratorset a private class

This class is not supposed to be used outside revset.py since it only
wraps content that is used by baseset typed classes.

It only gets created by revset operations or private methods.

mercurial/revset.py

@@ -70,7 +70,7 b' def _revdescendants(repo, revs, followfi'
                         yield i
                         break
 
-    return ascgeneratorset(iterate())
+    return _ascgeneratorset(iterate())
 
 def _revsbetween(repo, roots, heads):
     """Return all paths between roots and heads, inclusive of both endpoint
@@ -2391,9 +2391,14 b' class _generatorset(object):'
                 continue
         self._genlist.sort(reverse=reverse)
 
-class ascgeneratorset(_generatorset):
-    """ Same structure as _generatorset but stops iterating after it goes past
+class _ascgeneratorset(_generatorset):
+    """Wrap a generator of ascending elements for lazy iteration
+
+    Same structure as _generatorset but stops iterating after it goes past
     the value when asked for membership and the element is not contained
+
+    This class does not duck-type baseset and it's only supposed to be used
+    internally
     """
     def __contains__(self, x):
         if x in self._cache: