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/Lib/mhlib.py b/Lib/mhlib.py
index 9af04b2..df538f2 100644
--- a/Lib/mhlib.py
+++ b/Lib/mhlib.py
@@ -627,7 +627,7 @@
                     pass
 
     def removefromallsequences(self, list):
-        """Remove one or more messages from all sequeuces (including last)
+        """Remove one or more messages from all sequences (including last)
         -- but not from 'cur'!!!"""
         if hasattr(self, 'last') and self.last in list:
             del self.last