(ipv6_net_to_num, scm_from_ipv6): Renamed

(ipv6_net_to_num, scm_from_ipv6): Renamed
ipv6_net_to_num to scm_from_ipv6, for converting from an IPv&
byte-wise address to a SCM integer.  Changed all uses.
(ipv6_num_to_net, scm_to_ipv6): Renamed ipv6_num_to_net to
scm_to_ipv6 and added type and range checking, for converting from
an IPv& byte-wise address to a SCM integer.  Changed all uses.
(bignum_in_ipv6_range_p, VALIDATE_INET6): Removed, their function
is now done by scm_to_ipv6.

* validate.h, deprecated.h (SCM_VALIDATE_INUM, SCM_VALIDATE_INUM_COPY,
SCM_VALIDATE_BIGINT, SCM_VALIDATE_INUM_MIN,
SCM_VALIDATE_INUM_MIN_COPY,
SCM_VALIDATE_INUM_MIN_DEF_COPY,SCM_VALIDATE_INUM_DEF,
SCM_VALIDATE_INUM_DEF_COPY, SCM_VALIDATE_INUM_RANGE,
SCM_VALIDATE_INUM_RANGE_COPY): Deprecated because they make the
fixnum/bignum distinction visible.  Changed all uses to scm_to_size_t
or similar.