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/rgbimgmodule.c b/Modules/rgbimgmodule.c
index 4b0af22..a883f6a 100644
--- a/Modules/rgbimgmodule.c
+++ b/Modules/rgbimgmodule.c
@@ -553,7 +553,7 @@
  *	represents one pixel.  xsize and ysize specify the dimensions of
  *	the pixel array.  zsize specifies what kind of image file to
  *	write out.  if zsize is 1, the luminance of the pixels are
- *	calculated, and a sinlge channel black and white image is saved.
+ *	calculated, and a single channel black and white image is saved.
  *	If zsize is 3, an RGB image file is saved.  If zsize is 4, an
  *	RGBA image file is saved.
  *