Switching between HTML and visiual views destroys some table markup

[mdawaffe]

To reproduce:

1. Enter the following into HTML view (formerly known as "Code view").

   <table border="1" width="100%">
   	<tr>
   		<th align="center">Centered</th>
   		<th>Heading 1</th>
   		<th>Heading 2</th>
   	</tr>
   
   	<tr bgcolor="#cccccc">
   		<td><b>Bold</b></td>
   		<td>Foo</td>
   		<td>Bar</td>
   	</tr>
   </table>
   

2. Switch to Visual view.
3. Switch back to HTML view.
4. Notice that the second TR is gone.

This is caused by a bad regex in the JS that converts between the two views.

Patch attached.

[ryan]

(In [6547]) Don't bust table markup when switching between visual and html. Props mdawaffe. fixes #5577