Fix $DISPLAY being set to wrong value
Issue #79 (closed), MR!52
gdk_display_get_name () returns $WAYLAND_DISPLAY on Wayland environment. This value was set to $DISPLAY, which breaks programs that don't support Wayland. Now exo_execute_preferred_application_on_screen () gets $DISPLAY from the environment if necessary.
Edited by Yongha Hwang