guile 1.6 support

[Richard Frith-Macdonald]

I finally got round to it ... and modified gstep-guile, greg, and the 
GNUstep testcases to work with guile-1.6
All the changes are in CVS ... I spent a long time getting everything 
to work with the new module system in guile-1.6
Everything *should* still work with guile 1.4

I'd appreciate it if anyone interested could test the new code from CVS 
in both guile 1.4 environments (I don't want to break backward 
compatibility) and in a guile 1.6 environment, and let me know about 
any problems.

Once everything is stable, we can make a formal release I suppose.