Fix SF bug #479186: compiler generates bad code for "del"

Fix by Neil Schemenauer.  Visit the Subscript node when trying to find
the operation for a statement.

XXX Not sure if there are other nodes that should be visited.

Lib/compiler/pycodegen.py

@@ -1333,6 +1333,7 @@ def visitAssName(self, node):
         elif self.op != node.flags:
             raise ValueError, "mixed ops in stmt"
     visitAssAttr = visitAssName
+    visitSubscript = visitAssName
 
 class Delegator:
     """Base class to support delegation for augmented assignment nodes