Merge remaining changes from #813 into stable

Most of the changes made for pull request #813 were editorial or
were specific to authoring and thus did not require any changes
to Core AAM or testing related to exit criteria. Two of the changes,
however did not fall into this category namely:

* Make aria-valuetext a supported property of spinbutton
* Change the default value of aria-valuenow from 0 to "there is no
  current value"

Once we have ensured mapping changes have been made, tests are in
place, and implementations present or planned, we can merge the above
into the stable branch.

index.html

@@ -6668,6 +6668,7 @@ <h5>Presentational Roles Conflict Resolution</h5>
 								<li><pref>aria-valuemax</pref></li>
 								<li><pref>aria-valuemin</pref></li>
 								<li><pref>aria-valuenow</pref></li>
+								<li><pref>aria-valuetext</pref></li>
 							</ul>
 						</td>
 					</tr>
@@ -6700,6 +6701,7 @@ <h5>Presentational Roles Conflict Resolution</h5>
 						<td class="implicit-values">
 							Default for <pref>aria-valuemin</pref> is that there is no minimum value.<br/>
 							Default for <pref>aria-valuemax</pref> is that there is no maximum value.<br/>
+							Default for <pref>aria-valuenow</pref> is that there is no current value.<br/>
 						</td>
 					</tr>
 				</tbody>