Spelling fixes supplied by Rob W. W. Hooft. All these are fixes in either
comments, docstrings or error messages. I fixed two minor things in
test_winreg.py ("didn't" -> "Didn't" and "Didnt" -> "Didn't").

There is a minor style issue involved: Guido seems to have preferred English
grammar (behaviour, honour) in a couple places. This patch changes that to
American, which is the more prominent style in the source. I prefer English
myself, so if English is preferred, I'd be happy to supply a patch myself ;)
diff --git a/Modules/md5c.c b/Modules/md5c.c
index e747725..e6e7898 100644
--- a/Modules/md5c.c
+++ b/Modules/md5c.c
@@ -143,7 +143,7 @@
 }
 
 /* MD5 finalization. Ends an MD5 message-digest operation, writing the
-   the message digest and zeroizing the context.
+  the message digest and zeroing the context.
  */
 void
 MD5Final(unsigned char digest[16], MD5_CTX *context)