Bug#718954: Bug#717650: glx-diversions: There is only one alternative in link group glx

[Vincent Cheng]

# no longer sure if my proposed fix is actually what's needed, so revert title
retitle 717650 glx-diversions: There is only one alternative in link group glx
reopen 717650
thanks

I think my initial diagnosis was mistaken. Neither
glx-alternatives-mesa nor libgl1-mesa-glx are removed as part of the
upgrade to glx-alternatives in experimental. What needs to be done to
fix this manually is to reinstall libgl1-mesa-glx and to run
update-alternatives to re-select mesa-diverted as preferred
alternative for glx (see #712304 [1] or upstream github ticket [2]).
At this point I'm still unsure why reinstalling libgl1-mesa-glx helps
to fix this.

Vincent

[1] http://bugs.debian.org/712304
[2] https://github.com/Bumblebee-Project/Bumblebee/issues/452#issuecomment-22231887