--preresolve is not documented

[cron2]

we have an option --preresolve which change DNS resolution behaviour from "on demand" to "resolve all at startup" (if I read the code right, @schwabe ?). This is not a new option, but it escaped documentation so far... neither --help nor man page list it.

[cron2]

commit e719a05
Author: Arne Schwabe arne@rfc2549.org
Date: Sun Mar 23 13:13:06 2014 +0100

Introduce an option to resolve dns names in advance for --remote, --local and --http-proxy