Use `verify' to ensure that our hard-coded

Use `verify' to ensure that our hard-coded
bytes_to_*_digits arrays are long enough.  Of course, 17+-byte
integral types aren't on the near horizon, but just in case...
(MAX_INTEGRAL_TYPE_SIZE): Move definition to precede new first use.
(bytes_to_oct_digits, bytes_to_signed_dec_digits):
(bytes_to_unsigned_dec_digits, bytes_to_hex_digits): Change base
type from `char' to the clearer `unsigned int'.