Edit the gdm default file:

Code:
sudo gedit /etc/gdm/Init/Default
Look at the end of the file for:
Code:
      fi
    fi
  fi
fi

exit 0
Add the touch command:
Code:
      fi
    fi
  fi
fi

touch /var/tmp/testgdm

exit 0
Reboot your computer and look for the /var/tmp/testgdm if it exist:
Code:
ls -alg /var/tmp/testgdm
If the file doesn't exist, then the gdm default is not executed, meaning the code you have added from the first post is also not executed.

Pls note this is to verify the file /etc/gdm/Init/Default is executed, so the coded provided in the first post is also executed.