Renamed (undocumented) attribute overlay to overlayed on the environment
because it was clashing with a method of the same name.  The new attribute
is called "overlayed".

--HG--
branch : trunk
diff --git a/jinja2/environment.py b/jinja2/environment.py
index 9b3193a..569b9b3 100644
--- a/jinja2/environment.py
+++ b/jinja2/environment.py
@@ -191,7 +191,7 @@
     sandboxed = False
 
     #: True if the environment is just an overlay
-    overlay = False
+    overlayed = False
 
     #: the environment this environment is linked to if it is an overlay
     linked_to = None
@@ -303,7 +303,7 @@
 
         rv = object.__new__(self.__class__)
         rv.__dict__.update(self.__dict__)
-        rv.overlay = True
+        rv.overlayed = True
         rv.linked_to = self
 
         for key, value in args.iteritems():