* ui/aboutdialog.glade (label_debian_*): Remove.  The Debian
package of regexxer is not the only one out there, and I cannot
list all of them in the about dialog.  Sorry Ross :/
(label_translator_{what,who}): Give credit to the translator(s)
for the user's locale as listed in the translation of the string
"translator-credits".
(label_url): Get rid of the custom SelectableLabel widget class.
The only feature provided by the custom widget was tab-navigation
to labels -- I figured one can simply use C-Tab to do just that.
(label_author_who): ditto
(label_translator_who): ditto.

* src/aboutdialog.cc (SelectableLabel): Remove custom widget.
(AboutDialog::create): Acommodate to glade file modifications.