check if Origin matches Host to mitigate CSRF, part of #40
fix unittests
use Referer instead of Origin when using IE

  * IE10 (and 11) do not send HTTP_ORIGIN when requesting a URL no in
    the same origin, although recommended by WHATWG [1]
  * if IE10 is used, use the referer. If this header is supressed by the
    user, it won't work (and I don't care).

IE10 needs to die, seriously:

> We have a long-standing interoperability difference with other browsers
> where we treat different ports as same-origin whereas other browsers
> treat them as cross-origin.

via https://connect.microsoft.com/IE/feedback/details/781303/origin-header-is-not-added-to-cors-requests-to-same-domain-but-different-port

[1] http://tools.ietf.org/html/draft-abarth-origin-09
use el.getAttribute instead of el.dataset to support IE10 m(
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