Load xsession from XDG_DATA_DIRS not hardcoded at compile time

[David Edmundson]

It's perfectly reasonable for session desktop files to be in both /usr/local/xsessions and /usr/share/xsessions , and both paths should be searched in order.

It should also use XDG_DATA_DIRS environment variable to determine this path. Though it's up to your code to implement the following from freedesktop spec [1]
"If $XDG_DATA_DIRS is either not set or empty, a value equal to /usr/local/share/:/usr/share/ should be used."

[1] http://standards.freedesktop.org/basedir-spec/basedir-spec-0.5.html

[David Edmundson (david.edmundson)]

Turns out this isn't this simple: Feedback when testing on Chakara, is that sessions are in /etc/X11/sessions.

Loading from XDG_DATA_DIRS would actually break in these cases.