* configure.ac: Check for inet_ntop.
* m4/libcurl.m4: Provide a #define for the version of the curl
library.
* keyserver/gpgkeys_hkp.c (main, srv_replace): Call getaddrinfo() on
each target. Once we find one that resolves to an address (whether
IPv4 or IPv6), pass it into libcurl via CURLOPT_RESOLVE using the
SRV name as the "host". Force the HTTP Host header to be the same.
Autoconf 2.68 is more picky about correct macro usage and thus I need
to fix some wrong call conventions for AC_LANG_PROGRAM. Also factor
out an m4 conditional construct from AC_INIT to avoid the "not a
literal" warning.
