[PATCH] Remove all traces of reg_char.

[Roland McGrath]

The {u,}int_fastN_t types can be used in data structures as well as for
variables.  Also, they are required to be at least as large as intN_t but
may be larger, whereas intN_t are exact types so you know exactly how
overflow works and so forth.  So the intent is that on machines where
e.g. subword memory access is much more expensive than full-word access,
the fastN types might all be no smaller than a word.