Fix a few small issues. opening() is introduced later.

pep-0343.txt

@@ -98,7 +98,7 @@ Motivation and Summary
 
     Now consider this example:
 
-        with f = opening("/etc/passwd"):
+        with f = open("/etc/passwd"):
             BLOCK1
         BLOCK2
 
@@ -781,7 +781,7 @@ Examples
          indentation:
 
          class nested(object):
-             def __init__(*contexts):
+             def __init__(self, *contexts):
                  self.contexts = contexts
                  self.entered = None