Share xfce4-session and xfce4-power-manager code

[Ali Abdallah]

Hello,

1) org.freedesktop.PowerManagement is no longer mantained as a spec, it 
is removed from gpm, so using xfpm for these operation will force people 
to use xfpm always with Xfce... I still have the implementation for the 
moment but i'll remove the code in the future.

2) Personally i have no problem at all in having xfpm depending on 
xfce4-session, but lot of people uses xfpm with other desktops, we 
should think about those also.

3) I remember I already had this discussion with Brian, i think we end 
up in thinking about on small service+library that can be used from xfpm 
and the session, this means increasing the number of core modules.

There is no ideal solution for this, but i think the last option is the 
best, it also allows us to solve 
http://bugzilla.xfce.org/show_bug.cgi?id=6019 and to have more 
consitency between xfce products.

In any case i'm ready to help on this.

Cheers,
Ali.