suspend/hibernate support in xfce4-session

[Brian J. Tarricone]

Hi all,

I just committed suspend/hibernate support for xfce4-session, based on
a patch from Xubuntu (recently updated by Michael Casadevall).  I can't
test this myself (susp/hibernate doesn't work on my laptop), so please
give it a quick test if you can before beta2.

There's also quite a bit of new error-reporting code in there as well;
hopefully you don't run into it, but if you do, please note the
contents of the error dialog you get.

	-brian