[LightDM] Version 1.2.0 released

[Robert Ancell]

Overview of changes in lightdm 1.2.0

    * Backup .xsession-errors on login
    * Handle failures in pam_setcred
    * Open log files in append mode
    * Add extra checks in liblightdm so that it doesn't send invalid messages
      to the daemon
    * Fix gdmflexiserver not being added to the path (broken since 1.1.4)
    * Fix PAM conversations after authentication from locking up sessions
    * Fix PAM informational messages locking up autologin
    * Change XDMCP manage timeout from 10ms to 126s (maximum specified in the
      XDMCP specification)