Fixes for building under Mirage 2.1.x
Merge pull request #60 from avsm/master

Fixes for building under Mirage 2.1.x
Merge branch 'master' of https://github.com/mirage/mirage-skeleton

Conflicts:
	conduit_server/config.ml
	conduit_server_manual/config.ml
	dns/config.ml
	ethifv4/config.ml
	ethifv4/unikernel.ml
ping: add `tcpip` as opam dependency