James M Leddy authored Aug 23, 2011 and Howard Chu committed Jul 21, 2014

From RFC 2782:

  A client MUST attempt to contact the target host with the
  lowest-numbered priority it can reach.

This patch sorts the DNS SRV records by their priority, and
additionally gives records with a larger weight a higher probability
of appearing earlier. This way, the DNS SRV records are tried in the
order of their priority.

-       p += sizeof(HEADER);
+       p += NS_HFIXEDSZ;

(don't check what we expect applications to check).

Application is responsible for providing valid session pointers.

Update configure and depend --enable-dnssrv upon finding res_query
Update back-dnssrv to better handle ManageDSAit control