Original hack by Stefan Leuenberger <Stefan.Leuenberger@netmodule.com>.

The hack reprioritizes the SRV records used with transaction in case a
server refuses connection or it does not answer.

New functions sres_cache_set_srv_priority() and
sres_set_cached_srv_priority().

darcs-hash:20080111171223-65a35-be722d766d41da438d2bd6fe517fdc9169349755.gz