utils/macros.h: Add <ctype.h> and `foocmp' helper macros.

Both of these have been a nuisance for years.  Do something about it.

The command

	git grep -En '\<(is|to)[a-z]+\(|\<(str|mem)[a-z]*cmp\(' -- '*.[ch]'

finds code which it might be good to change.

The hairy Emacs command

	(query-replace-regexp
	 "\\<\\(\\(str\\|mem\\)\\sw*cmp\\)(\\([^,]*\\), \\([^)]*\\)) \\(==\\|!=\\|<\\|<=\\|>\\|>=\\) 0"
	 '(replace-eval-replacement
	   . (concat (replace-quote (upcase (match-string 1)))
		     "(\\3, \\5, \\4)"))
	 nil
	 (if (and transient-mark-mode mark-active) (region-beginning))
	 (if (and transient-mark-mode mark-active) (region-end))
	 nil)

will convert easy cases of `foocmp' calls, but hard ones have to be done
by hand.