[Bug 29404] gdm should support alternate config file for cdd branding

[Oliver Grawert]

Public bug reported:
https://launchpad.net/malone/bugs/29404

Affects: gdm (Ubuntu)
       Severity: Normal
       Priority: (none set)
         Status: Unconfirmed

Description:
currently gdm doesnt support rebranding through other artwork packages,
the attached patch adds a check for a /etc/gdm/gdm-cdd.conf file that
can be installed from a artwork metapackage if rebranding for a cdd
distribution is desired.