Improve check.php: use CSS to style and output complete page

Errors now get reported in check.php using
<font color="red"><b>Message</b></font>

I propose implementing this with: <strong
class="errorMessage">Message</strong>

And furthermore style the <strong> in style.css of the
themes with:

.errorMessage {
color: red;
}

But since style.css is normally not included yet when
an error in check.php occurs, it has to be included in
the output page of check.php errors:
<link href="themes/standard/style.css" rel="stylesheet"
type="text/css" />. Moreover, you also want check.php
to return a valid total XHTML 1.1 page including header
and body tags, so these have to be added too. Putting
argument of the similar error "echo's" in check.php in
a function seems logical.

NOCC 1.3-dev (CVS build 2006-10-16)