Enable access() when building in Visual Studio

Enable access() when building in Visual Studio

Visual Studio does not enable certiain standard Unix functions,
such as access().  By defining _CRT_NONSTDC_NO_WARNINGS and
_CRT_SECURE_NO_WARNINGS, these functions are enabled.

This patch also adds a ./configure check for access() as well,
in case this needs to be implemented on other platforms lacking
this feature.  Which is why HAVE_ACCESS is defined in win/config.h.in

Thanks to Alon Bar-Lev for helping solving this.

Signed-off-by: David Sommerseth <davids@redhat.com>
Acked-by: Alon Bar-Lev <alon.barlev@gmail.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
URL: http://thread.gmane.org/gmane.network.openvpn.devel/5179/focus=5200