Build with -mno-red-zone on x86_64

Otherwise, an interrupt may overwrite part of the stack if we're in
checksum_stubs.c at the time. Should help with #80.

Also added -fno-stack-protector in case that's on by default somewhere.
Improve formatting of DHCP console logging, including printing out options.
Merge branch 'red-zone' of git://github.com/talex5/mirage-tcpip into 2.0.2-release
Sync changes for 2.0.2 release
Merge pull request #84 from avsm/2.0.2-release

2.0.2 release
Ipv6: Refactor
Ipv6: Improve log messages
Ndpv6: remove signatures from implementation
Ipv6: fix hop lim in pong packets
Ipv6: fix packet queueing order
Ipv6: move ndp_option to Parser.option
Ipv6: Clarify processing of RA options
Ndpv6: more precise signatures + some docs
Ipv6: more docs
Ipv6: implement `AddressList.handle_na`
Merge branch 'master' of https://github.com/mirage/mirage-tcpip

Conflicts:
	CHANGES
	myocamlbuild.ml
	setup.ml
Merge branch 'ipv6-refactor'