Errors compiling Bro on OpenBSD 2.9

The OpenBSD compile gets the following errors, relating to BIND defines
and such.

This is indeed a pain. Note that you can work around it by editing config.h
and turning off HAVE_NB_DNS and removing nb_dns.o from OBJ in the Makefile.

The autoconf code is supposed to detect this case already, but the test
it's using (checking for res_mkquery) isn't powerful enough - it fails
on several systems another is Mac OS X).