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/stropmodule.c b/Modules/stropmodule.c
index 612d0d3..62a17a3 100644
--- a/Modules/stropmodule.c
+++ b/Modules/stropmodule.c
@@ -167,7 +167,7 @@
 joinfields(list [,sep]) -> string\n\
 \n\
 Return a string composed of the words in list, with\n\
-intervening occurences of sep.  Sep defaults to a single\n\
+intervening occurrences of sep.  Sep defaults to a single\n\
 space.\n\
 \n\
 (join and joinfields are synonymous)";
@@ -1040,10 +1040,10 @@
 /*
    mymemreplace
 
-   Return a string in which all occurences of PAT in memory STR are
+   Return a string in which all occurrences of PAT in memory STR are
    replaced with SUB.
 
-   If length of PAT is less than length of STR or there are no occurences
+   If length of PAT is less than length of STR or there are no occurrences
    of PAT in STR, then the original string is returned. Otherwise, a new
    string is allocated here and returned.