Change createElement() namespace to match implementations

Fixes https://www.w3.org/Bugs/Public/show_bug.cgi?id=19431.

See comments 12 and 20 there. Gecko tried switching to the spec's
current wording and immediately had to back out due to extension
breakage. It does not seem likely the current spec is implementable.

dom.bs

@@ -4689,8 +4689,12 @@ invoked, must run these steps:
  <li>If <var>is</var> is non-null and <var>definition</var> is null, then <a>throw</a> a
  {{NotFoundError}}.
 
+ <li>Let <var>namespace</var> be the <a>HTML namespace</a>, if the <a>context object</a>'s
+ <a for=Document>content type</a> is "<code>text/html</code>" or
+ "<code>application/xhtml+xml</code>", and null otherwise.
+
  <li>Let <var>element</var> be the result of <a>creating an element</a> given the
- <a>context object</a>, <var>localName</var>, null, the <a>HTML namespace</a>, <var>is</var>, and
+ <a>context object</a>, <var>localName</var>, null, <var>namespace</var>, <var>is</var>, and
  with the <var>synchronous custom elements</var> flag set. Rethrow any exceptions.
 
  <li>If <var>is</var> is non-null, then <a>set an attribute value</a> for <var>element</var> using

dom.html

@@ -71,7 +71,7 @@
    <p data-fill-with="logo"><a class="logo" href="https://whatwg.org/"> <img alt="WHATWG" height="100" src="https://resources.whatwg.org/logo-dom.svg"> </a> </p>
    <hgroup>
     <h1 class="p-name no-ref allcaps" id="title">DOM</h1>
-    <h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="content">Living Standard — Last Updated <time class="dt-updated" datetime="2016-04-11">11 April 2016</time></span></h2>
+    <h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="content">Living Standard — Last Updated <time class="dt-updated" datetime="2016-04-13">13 April 2016</time></span></h2>
    </hgroup>
    <div data-fill-with="spec-metadata">
     <dl>
@@ -2603,7 +2603,9 @@ <h3 class="heading settled" data-level="4.5" id="interface-document"><span class
  such member exists. 
     <li>Let <var>definition</var> be the result of <a data-link-type="dfn" href="https://rawgit.com/w3c/webcomponents/15a203c8393aef0df7223ab1d43406aa11a7e71e/spec/custom/index.html#dfn-look-up-custom-element-definition">looking up a custom element definition</a>, given the <a data-link-type="dfn" href="#context-object">context object</a>, the <a data-link-type="dfn" href="#html-namespace">HTML namespace</a>, <var>localName</var>, and <var>is</var>. 
     <li>If <var>is</var> is non-null and <var>definition</var> is null, then <a data-link-type="dfn" href="https://heycam.github.io/webidl/#dfn-throw">throw</a> a <code class="idl"><a data-link-type="idl" href="https://heycam.github.io/webidl/#notfounderror">NotFoundError</a></code>. 
-    <li>Let <var>element</var> be the result of <a data-link-type="dfn" href="#concept-create-element">creating an element</a> given the <a data-link-type="dfn" href="#context-object">context object</a>, <var>localName</var>, null, the <a data-link-type="dfn" href="#html-namespace">HTML namespace</a>, <var>is</var>, and
+    <li>Let <var>namespace</var> be the <a data-link-type="dfn" href="#html-namespace">HTML namespace</a>, if the <a data-link-type="dfn" href="#context-object">context object</a>’s <a data-link-type="dfn" href="#concept-document-content-type">content type</a> is "<code>text/html</code>" or
+ "<code>application/xhtml+xml</code>", and null otherwise. 
+    <li>Let <var>element</var> be the result of <a data-link-type="dfn" href="#concept-create-element">creating an element</a> given the <a data-link-type="dfn" href="#context-object">context object</a>, <var>localName</var>, null, <var>namespace</var>, <var>is</var>, and
  with the <var>synchronous custom elements</var> flag set. Rethrow any exceptions. 
     <li>If <var>is</var> is non-null, then <a data-link-type="dfn" href="#concept-element-attributes-set-value">set an attribute value</a> for <var>element</var> using
  "<code>is</code>" and <var>is</var>.