1.28.0

• Continue to shutdown session is removing X authority fails
• Set XDG_SEAT env variable in script hooks
• Fix small leak in XDMCP server
• liblightdm-qt: mark class PowerInterface as exported
• Fix one qt5 test being run instead of a qt4 one
• Remove use of deprecated g_type_class_add_private
• Modernize private data in objects
• Document XDG_SEAT_PATH in man page
• Fix install failing if link already exists
• Remove bashisms in configure.ac