This is a bug in Qt4, then - libgl1-mesa was obsoleted by libgl1-mesa-
glx on Edgy.
** Changed in: xorg (Ubuntu)
Status: Unconfirmed => Rejected
** Also affects: qt4-x11 (Ubuntu)
Importance: Untriaged
Status: Unconfirmed
--
xorg_1:7.0.22ubuntu7 depends on specific libgl1-mesa
https://launchpad.net/bugs/54560