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.
diff --git a/Lib/compiler/pycodegen.py b/Lib/compiler/pycodegen.py
index 88767a4..83e6433 100644
--- a/Lib/compiler/pycodegen.py
+++ b/Lib/compiler/pycodegen.py
@@ -1333,6 +1333,7 @@
         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