If you've got a headline where the text is a link, C-c C-c on that
headline will only consider the fact that it's in a link, not that it's
in a headline. Ie, you get "can do nothing useful", rather than setting
tags.

This patch checks for this condition and passes the C-c C-c to the
headline.

An alternate version would pass the funcall to the :parent element *no
matter what*, seeing as 'C-c C-c' is currently always a no-op, and
user-defined hooks have already been run. We could just pass it on up
and see what happens...

Eric