Fix typo reported by Tony Nelson.

pep-0353.txt

@@ -178,7 +178,7 @@ An initial attempt to implement this feature tried to use
 size_t. It quickly turned out that this cannot work: Python
 uses negative indices in many places (to indicate counting
 from the end). Even in places where size_t would be usable,
-to many reformulations of code where necessary, e.g. in
+too many reformulations of code where necessary, e.g. in
 loops like::
 
   for(index = length-1; index >= 0; index--)