assume res_init() is always there.

assume res_init() is always there.

Previously, the code tried to find res_init(), and on some systems
got it wrong in configure, silently not-using res_init(), leading
to unexpected failures to re-init the resolver.

We know that all supported OSes (except Windows) have res_init(), so
change the call to "#ifndef WIN32", and adjust configure.ac to just
find the library to link (if any).  With that, failures to find
res_init() are no longer "hidden" but clearly visible at link time.

AC_SEARCH_LIBS() bits inspired by CUPS' cups_network.m4 (GPLv2)

Fix (part of) trac #523

Signed-off-by: Gert Doering <gert@greenie.muc.de>
Lazy-ACK-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <1430162841-5840-1-git-send-email-gert@greenie.muc.de>
URL: http://article.gmane.org/gmane.network.openvpn.devel/9614
(cherry picked from commit 403dc434d245e5df5ae262935aa2e7364547e260)