basectx: move dirty from changectx

mercurial/context.py

@@ -145,6 +145,9 b' class basectx(object):'
     def dirs(self):
         return self._dirs
 
+    def dirty(self):
+        return False
+
 class changectx(basectx):
     """A changecontext object makes access to data related to a particular
     changeset convenient. It represents a read-only context already presnt in
@@ -406,9 +409,6 b' class changectx(basectx):'
             if match.bad(fn, _('no such file in rev %s') % self) and match(fn):
                 yield fn
 
-    def dirty(self):
-        return False
-
 class filectx(object):
     """A filecontext object makes access to data related to a particular
        filerevision convenient."""