Move private file access checks to options_postprocess_filechecks()

Move private file access checks to options_postprocess_filechecks()

This removes the dependency of crypto.c on misc.c, which makes testing
(stuff that needs) crypto.c functionality easier.

Apart from that, testing file access really belongs in
options_postprocess_filechecks(), and moving it there enables us to
perform the same check for other private files too.

v2: change indenting, remove remaining warn_if_group_others_accessible()
    calls and move function to options.c.

[ DS: This patch is a slightly modified version of the one sent to the
     mailing list. It removes all references to --tls-crypt, so it
     can be applied eariler to the tree as it contains a good clean-up
     as well ]

Signed-off-by: Steffan Karger <steffan.karger@fox-it.com>
Acked-by: David Sommerseth <davids@openvpn.net>
Message-Id: <1479045751-22297-1-git-send-email-steffan.karger@fox-it.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg13019.html
Signed-off-by: David Sommerseth <davids@openvpn.net>