+PH/16 It seems that the options setting for the resolver (RES_DEFNAMES and
+ RES_DNSRCH) can affect the behaviour of gethostbyname() and friends when
+ they consult the DNS. I had assumed they would set it the way they
+ wanted; and indeed my experiments on Linux seem to show that in some
+ cases they do (I could influence IPv6 lookups but not IPv4 lookups).
+ To be on the safe side, however, I have now made the interface to
+ host_find_byname() similar to host_find_bydns(), with an argument
+ containing the DNS resolver options. The host_find_byname() function now
+ sets these options at its start, just as host_find_bydns() does. The smtp
+ transport options dns_qualify_single and dns_search_parents are passed to
+ host_find_byname() when gethostbyname=TRUE in this transport. Other uses
+ of host_find_byname() use the default settings of RES_DEFNAMES
+ (qualify_single) but not RES_DNSRCH (search_parents).
+