Change all chars being passed to the ctype macros (isalph(), etc.) to

Change all chars being passed to the ctype macros (isalph(), etc.) to
be unsigned chars, following through to change any other types as
necessary (e.g. comparison between two pointers). Not all chars have
been changed to unsigned chars; just those that were in danger of being
sign extended when passed to the int-taking ctype macros.