initial DNS packet support
add DNS resource records
add str to depends for DNS
need this from the IGMP support
will create an easily resolved merge conflict later
set length of DNS RR sections
Merge branch 'dns_support' of github.com:adferguson/ocaml-packet into adferguson-dns_support

Conflicts:
	_oasis
	_tags
	lib/META
	setup.ml