Pages under templates/ are invalid (in fact, not only invalid, but also not well-formed) xhtml pages.

This problem is especially serious when you change extension from .html to
.xhtml in ikiwiki.setup and use Firefox. Since Firefox will display a error
message only for not well-formed application/xhtml+xml pages.

It seems that HTML::Template also support `<!--Variable-->` syntax instead
of `<Variable>`.  Chaning to this syntax will solve this problem, I guess.


Even if changed to `<!-- TMPL_VAR -->` style, the problem may still exist if the template contains if else block.

Maybe just encode all &lt; and &gt; when compling pages within the templates folder will solve this problem.

> I never noticed this bug, since it only happens if the htmlscrubber is
> disabled. --[[Joey]]
