XHTML conformance tweaks

Hello,

validator.w3.org complains about 2 things:

• id=navlist is used more than once (if you use more than one menu, that is), can be fixed by using a class instead
• the heading1 of the site-header is inside a heading1, which looks like it was forgotten when editing, because there is also a double check on if ($sitename)

Patch is attached, otherwise very nice theme, looks perfect even on 800x480 (Nokia770).

Kind regards
Spiney