Non-word characters don't terminate tag names.

The PHP sanitizer was including only \w+ in tag names.  This meant that
<b.foo> and <bä> were converted to <b> tags (bug 17663); <s.foo> and
<s-id> were treated as 
 tags (bug 40670), and <sub-ID#1> was treated
as a <sub> tag (bug 52022).  (But note that <strike> *is* actually a valid
synonym for 
.)

Fix the sanitizer.

Bug: 17663
Change-Id: Iceec404f46703065bf080dd2cbfed1f88c204fa5
Merge "Non-word characters don't terminate tag names."