Revert r35819 -- broke thumbnailing.

Revert r35819 -- broke thumbnailing.

  10 previously passing test(s) now FAILING! :(
      * Thumbnail image caption with a free URL  [Introduced between 03-Jun-2008 19:49:16, 1.13alpha (r35816) and 03-Jun-2008 23:42:22, 1.13alpha (r35827)]
      * BUG 1887: A ISBN with a thumbnail  [Introduced between 03-Jun-2008 19:49:16, 1.13alpha (r35816) and 03-Jun-2008 23:42:22, 1.13alpha (r35827)]
      * BUG 1887: A RFC with a thumbnail  [Introduced between 03-Jun-2008 19:49:16, 1.13alpha (r35816) and 03-Jun-2008 23:42:22, 1.13alpha (r35827)]
      * BUG 1887: A mailto link with a thumbnail  [Introduced between 03-Jun-2008 19:49:16, 1.13alpha (r35816) and 03-Jun-2008 23:42:22, 1.13alpha (r35827)]
      * BUG 1887: A <math> with a thumbnail- we don't render math in the parsertests by default,
so math is not stripped and turns up as escaped &lt;math&gt; tags.  [Introduced between 03-Jun-2008 19:49:16, 1.13alpha (r35816) and 03-Jun-2008 23:42:22, 1.13alpha (r35827)]
      * BUG 1887, part 2: A <math> with a thumbnail- math enabled  [Introduced between 03-Jun-2008 19:49:16, 1.13alpha (r35816) and 03-Jun-2008 23:42:22, 1.13alpha (r35827)]
      * Image caption containing another image  [Introduced between 03-Jun-2008 19:49:16, 1.13alpha (r35816) and 03-Jun-2008 23:42:22, 1.13alpha (r35827)]
      * Bug 3090: External links other than http: in image captions  [Introduced between 03-Jun-2008 19:49:16, 1.13alpha (r35816) and 03-Jun-2008 23:42:22, 1.13alpha (r35827)]
      * Width + Height sized image (using px) (height is ignored)  [Introduced between 03-Jun-2008 19:49:16, 1.13alpha (r35816) and 03-Jun-2008 23:42:22, 1.13alpha (r35827)]
      * <references> after <gallery> (bug 6164)  [Introduced between 03-Jun-2008 19:49:16, 1.13alpha (r35816) and 03-Jun-2008 23:42:22, 1.13alpha (r35827)]