Add support for block-outside-dns through the interactive service

Add support for block-outside-dns through the interactive service

- Add a new message type in openvpn-msg.h
- Pass msg_channel HANDLE to win_wfp_block_dns and win_wfp_uninit
- Add a handler in interactive.c for block_dns request

The service build now depends on block_dns.[ch] in src/openvpn

v2 changes:
- Make CmpEngine non-nested (be nice with non-gcc compilers)
- Print error code in hex

Signed-off-by: Selva Nair <selva.nair@gmail.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <1456457091-3872-2-git-send-email-selva.nair@gmail.com>
URL: http://article.gmane.org/gmane.network.openvpn.devel/11265
Signed-off-by: Gert Doering <gert@greenie.muc.de>