Rename class ContextManager to ContextWrapper, per Nick's proposal.

pep-0343.txt

@@ -258,7 +258,7 @@ Generator Decorator
     that makes it possible to use a generator that yields exactly once
     to control a with-statement.  Here's a sketch of such a decorator:
 
-        class ContextManager(object):
+        class ContextWrapper(object):
 
            def __init__(self, gen):
                self.gen = gen
@@ -287,14 +287,14 @@ Generator Decorator
 
         def contextmanager(func):
            def helper(*args, **kwds):
-               return ContextManager(func(*args, **kwds))
+               return ContextWrapper(func(*args, **kwds))
            return helper
 
     This decorator could be used as follows:
 
         @contextmanager
         def opening(filename):
-           f = open(filename) # IOError is untouched by ContextManager
+           f = open(filename) # IOError is untouched by ContextWrapper
            try:
                yield f
            finally: