GtkAboutDialog: Fix a corner case of link highlighting

GtkAboutDialog: Fix a corner case of link highlighting

GtkAboutDialog highlights emails written as <...> and
urls written as http://... . gnome-terminal manages to
put <http://...> into its license text, which sadly
confuses the parser into running evolution on http://...

Fix things up far enough that <http://...> is now
recognized as url, and only the part inside the <> is
underlined (for email addresses, we include the <> in
the underline).