Bug#2879: gwm uses Pre-Depends

[Ian Jackson <ian@chiark.chu.cam.ac.uk>]

Package: gwm
Version: 1.8c-2

 Package: gwm
 version: 1.8c-2
 pre-depends: libc5 (>=5.2.18-1), xlib(>=3.1.2-4), xpm4.7(>=3.4g-2)
 ...

Only base packages should use Pre-Depends.

Ian.