Changes to encodings of NSSliderCell and NSParagraphStyle

[Fred Kiefer]

I had to change the encoding of NSSliderCell and NSParagraphStyle in the 
gui library to accommodate new attributes. This changes are of course 
backward compatible (i.e. with new libraries you are still able to read 
old archives), but not forward compatible (applications using old 
libraries wont be able to read the new archives). If you are using the 
GNUstep CVS or a current snapshot, please make sure that you update all 
your GNUstep installations at once. It is a rather uncommon scenario to 
exchange objects of these two object classes, but who knows.

Judging from the comments I did find in other classes encoding methods 
there will be a lot more incompatible changes for gui classes. Hopefully 
we get the archiving of them all sorted out for the next release to save 
us all further warning mails.

Fred