Fix #380: Require a javascript content-type.
Be more precise about how to get the mime type for a fetched script.
Merge pull request #394 from jyasskin/js-content-type

Fix #380: Require a javascript content-type.
Thanks! @annevk It seems "one of" is used with both "and" and "or". e.g. http://www.whatwg.org/specs/web-apps/current-work/multipage/syntax.html#parsing-main-inhtml