Doxygen errors in theme.inc

The theme system doxygen group start marker disappeard due to some recent commit...

- * @defgroup themeable Themeable functions
- * @{

This should go in again... I don't know how it iterferes with the @file rule though, so I am not confident on what to add/remove from the comments. Someone who knows better please provide a patch. Or is this was intentional (which is suggested by the link to the themeable group on the top of the file), then the '@endgroup themeable' clause at the end should be removed... I thought that the theme functoins defined in theme.inc are supposed to be in the themeable group...