If you try to upgrade to a new version of gdm when scrollkeeper isn't installed, the postinstall script will fail because scrollkeeper-update doesn't exist, which means that the upgrade will fail and leave both versions of gdm sitting around on your computer. Either the gdm RPM needs to have a dependency on scrollkeeper, or the postinstall and postuninstall scripts need to do "scrollkeeper-update || true" or something to avoid problems when scrollkeeper isn't installed.
there are more problems here than it seems - we are going to remove this package from rawhide for the time being