u_intN_t is dead, long live uintN_t.

And, as we require at least autoconf 2.61, and as autoconf 2.61 and
later have AC_TYPE_UINTn_T and AC_TYPE_INTn_T macros, we use them to
define the uintN_t and intN_t macros if the system doesn't define them
for us.

This lets us get rid of bitypes.h as well.
More getting rid of old u_intN_t.
Some indentation cleanups from the previous checkin.