mirage-www files are optional (and add xen version)
correct ocaml-version for camlp5 -- it works on 4.00.1
disable warnings as errors on why (fixes 4.00.1 compile hopefully)
add dns.0.6.2, fixes lwt compilation

Closes #392
add an impossible version for debug-camlp4-base as its only for dev use
Merge pull request #394 from mirage/master

more jenkins fixes