http: disallow sending obviously invalid status codes

Back port of
https://github.com/nodejs/node/commit/7e9b0dd6949aaa6afda4da9f41e1d60d9b
to v0.12

PR-URL: https://github.com/nodejs/node-private/pull/48


Reviewed-By: Fedor Indutny <fedor.indutny@gmail.com>
Reviewed-By: Rod Vagg <rod@vagg.org>