Log Message:
Fix the detection of bind on systems where it's available natively.
This bug was introduced in revision 1.7 where bind was determined to
be built-in only if libbind.* existed on the system, which isn't
necessarily true on systems where the resolver routines are incorporated
into libc, e.g. NetBSD.

We now consider bind to be built-in if BUILTIN_VERSION.bind is defined,
and we define BUILTIN_VERSION.bind only if /usr/sbin/named exists on
the system.  We also improve the derivation of the version number of
BIND by parsing the named output, so we can now also detect bind-4.x
and bind-8.x.