If you set a custom http header which includes eg. the string `Date`,
then http will not automatically send the `Date` header.
This is also true for other automatic http headers.
PR-URL: https://github.com/iojs/io.js/pull/828
Reviewed-By: Brendan Ashworth <brendan.ashworth@me.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
