The xsession script was called with inconsistent (depending on the
display managers) and wrong parameters. The main reason for this where
the spaces the parameter syntax. In order to fix this the old syntax:
$1 = '<desktop-manager> + <window-manager>'
Will be replaced with a new syntax:
$1 = "<desktop-manager>+<window-manager>"
This assumes that neither "<desktop-manager>" nor "<window-manager>"
contain the "+" character but this shouldn't be a problem.
This patch also fixes the quoting by using double quotes (") instead of
single quotes (') [0].
Last but not least this'll add some comments for the better
understanding of the script.
[0]: https://specifications.freedesktop.org/desktop-entry-spec/latest/ar01s06.html