GTK3-apps unusable with some themes

[Steff]

Problem
---------
If a theme without gtk-3-support is used, gtk-3-apps (evince, gedit etc.) are inusable: The scrollbars are ugly, parts of the UI for example tabs are black and one can hardly select any text.

If one changes the theme to one that doesn't support gtk3 it is obvious where the problem is coming from and users can simply change the theme back. But if a setup that doesn't use any gtk-3-apps and has a theme without gtk-3-support is updated and the newer version of as app uses gtk-3 it is very difficult to find out what's the problem.

Solution
---------
Things that should be changed:
*)
Mark themes not supporting gtk-3 in the theme-choser-dialogs

*)
Many themes are ported to support gtk-3. But the ported ones (that support gtk-2 and 3) are in different packages. The packages should be changed such that the ported ones replace the old ones. For example clearlooks-phenix-theme should replace clearlooks in gnome-themes-extra

Additionally one of the following schould also be done:
*)
Dependencies should be changed such that libgtk-3-0 is in conflict with all theme-packages that doesn't support gtk3

or

*)
The themes for gtk2 and gtk3 should get chosen seperately.

or

*)
There should be a usable fallback-gtk-3-theme that should automatically be used for gtk-3-apps if the chosen theme doesn't support gtk-3 itself.

[Steff (s-teff)]

Fix of this bug should also fix
https://bugs.launchpad.net/ubuntu/+source/xfce4/+bug/1050012

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.