fix packet encoding from 89322cbe8ee6414d4a668e6b957cc70d35d5a2bd
sync CHANGES
depend on ocaml4+ (use of `%revapply` in `Operators`)
Use a purely functional Map instead of an Hashtbl to store domain names (which are string list, eg. with a *very* bad hash function anyway)
Merge branch 'master' of git://github.com/mirage/ocaml-dns