Added support for optional `scoped` modifier to blocks.

--HG--
branch : trunk
diff --git a/jinja2/nodes.py b/jinja2/nodes.py
index 6383372..c7858b6 100644
--- a/jinja2/nodes.py
+++ b/jinja2/nodes.py
@@ -269,7 +269,7 @@
 
 class Block(Stmt):
     """A node that represents a block."""
-    fields = ('name', 'body')
+    fields = ('name', 'body', 'scoped')
 
 
 class Include(Stmt):