Document --preresolve option

Document --preresolve option

The option resolves configured remote, local, and proxy hostnames at
startup and reuses those resolved addresses on reconnects.

Document it in the usage text and client options man page, including
the reconnect trade-off for configurations that rely on changing DNS
answers.

GitHub: fixes OpenVPN/openvpn#532
Acked-by: Arne Schwabe <arne@rfc2549.org>
Message-Id: <_5bQ5LvkEmn_vaE7Ng8xPAcHJFWfy7td0Yvim0iLc3YVoer2RM1-PoBKAGPzHZKx1rsZP7Ht7kM_2eIUSidNkMW34yS7eT549_fSvcb-dl0=@pm.me>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg37387.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>