Favicon issue

The leftmost menu item showing the site's favicon normally displays extra adminstrative tasks. However, when a site is configured to not use any favicon at all, the menu item is completely inaccessible.

Attached patch fixes the code, but not the design. Instead of using "misc/arrow-asc.png" (a temporary fix) we should find a properly looking replacement image to display when the favicon has been disabled (or couldn't be found due to misconfiguration, check the implementation of theme_get_setting() if you're after the gory details). Status intentionally set to "needs work".