add a SETUP_WITH opcode

It speeds up the with statement and correctly looks up the special
methods involved.
diff --git a/Python/import.c b/Python/import.c
index 5e42e5c..88aced0 100644
--- a/Python/import.c
+++ b/Python/import.c
@@ -74,9 +74,10 @@
        Python 2.7a0: 62171 (optimize list comprehensions/change LIST_APPEND)
        Python 2.7a0: 62181 (optimize conditional branches:
 			    introduce POP_JUMP_IF_FALSE and POP_JUMP_IF_TRUE)
+       Python 2.7a0  62191 (introduce SETUP_WITH)
 .
 */
-#define MAGIC (62181 | ((long)'\r'<<16) | ((long)'\n'<<24))
+#define MAGIC (62191 | ((long)'\r'<<16) | ((long)'\n'<<24))
 
 /* Magic word as global; note that _PyImport_Init() can change the
    value of this global to accommodate for alterations of how the