[Fedora-haskell-list] guidelines install scripts

[Jens Petersen]

Thanks Tom,

> If you want to test the corner-case 
> that the old preinst/postun logic was added to handle, try the following:

Okay I tried this and it looks ok for me with the revised macros.

I had to fix an another error in the original macros while testing though though caused by using "&&" without "|| :" instead of "if" in %preun.
Luckily no released shipped packages have used it yet, since it breaks package updating. 

Jens