We use structures to pass information in all callbacks so we always get 3
arguments: parent, parameters, data
Also change the return type to int so we can catch errors when changing
session stati.
Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
The dummy session is a very simply session implementation that simply
draws a black background. It will be used by each seat as fallback if no
other session is available. If we didn't do that, we wouldn't be able to
guarantee that the screen is cleared after a session is unregistered.
Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
