Common gotchas upgrading from 4.0 -> 4.2

[Jasper Huijsmans]

Hey all,

I think it would be good if we could collect a list of common problems that
people may encounter when upgrading from 4.0 to 4.2. Some sort of Upgrading
FAQ.

- removal of workspaces mcs plugin: left-over old version interferes with new
  plugin.

- Base dir spec. Some distribution apparently set XDG_*_DIRS. If that does not
  include the Xfce prefix, none of the modules will find their configuration.

- Icon theme stuff. I know of two problems that seem to happen fairly often,
  missing icons when librsvg is not installed (slackware only?), and missing
  icons in nautilus. Not sure if we have a solution for those.

[Add more here]

	Jasper