Allow multiple context managers in one with statement, as proposed
in http://codereview.appspot.com/53094 and accepted by Guido.

The construct is transformed into multiple With AST nodes so that
there should be no problems with the semantics.
diff --git a/Misc/NEWS b/Misc/NEWS
index a6b5fce..daab366 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -12,6 +12,8 @@
 Core and Builtins
 -----------------
 
+- Added support for multiple context managers in the same with statement.
+
 - Issue #6101: A new opcode, SETUP_WITH, has been added to speed up the with
   statement and correctly lookup the __enter__ and __exit__ special methods.