Stop treating about URLs as same-origin

Browsers don’t implement about:blank as such and certainly don’t want
to implement about:config et al this way.

Thanks to mode “navigate” this change also doesn’t impact navigation,
where about:blank needs to remain same-origin.

It might impact <object>, but the current standard for that element is
known to be broken.

Fixes #384 and closes #385 by extension.

Overview.html

@@ -7,7 +7,7 @@
 
 <p><a class="logo" href="https://whatwg.org/"><img alt="WHATWG" height="100" src="https://resources.whatwg.org/logo-fetch.svg" width="100"></a>
 <h1 id="cors">Fetch</h1>
-<h2 class="no-num no-toc" id="living-standard-—-last-updated-31-august-2016">Living Standard — Last Updated 31 August 2016</h2>
+<h2 class="no-num no-toc" id="living-standard-—-last-updated-14-september-2016">Living Standard — Last Updated 14 September 2016</h2>
 
 <dl>
  <dt>Participate:
@@ -2487,10 +2487,6 @@ <h3 id="main-fetch"><span class="secno">5.1 </span>Main fetch</h3>
    <a class="external" data-anolis-spec="url" href="https://url.spec.whatwg.org/#concept-url-scheme" title="concept-url-scheme">scheme</a> is
    "<code title="">data</code>" and <var>request</var>'s
    <a href="#same-origin-data-url-flag">same-origin data-URL flag</a> is set
-   <dt><var>request</var>'s
-   <a href="#concept-request-current-url" title="concept-request-current-url">current url</a>'s
-   <a class="external" data-anolis-spec="url" href="https://url.spec.whatwg.org/#concept-url-scheme" title="concept-url-scheme">scheme</a> is
-   "<code title="">about</code>"
    <dt><var>request</var>'s <a href="#concept-request-mode" title="concept-request-mode">mode</a> is
    "<code title="">navigate</code>" or "<code title="">websocket</code>"
 

Overview.src.html

@@ -2417,10 +2417,6 @@ <h3>Main fetch</h3>
    <span data-anolis-spec=url title=concept-url-scheme>scheme</span> is
    "<code title>data</code>" and <var>request</var>'s
    <span>same-origin data-URL flag</span> is set
-   <dt><var>request</var>'s
-   <span title=concept-request-current-url>current url</span>'s
-   <span data-anolis-spec=url title=concept-url-scheme>scheme</span> is
-   "<code title>about</code>"
    <dt><var>request</var>'s <span title=concept-request-mode>mode</span> is
    "<code title>navigate</code>" or "<code title>websocket</code>"