replaced corpus literals by variables

Hi Maciej,

I'm doing some computational stylistics during the holidays...

The oppose script didn't use the primary.corpus.dir and secondary.corpus.dir variables.

Also, when using the chi-square zeta, the words_avoided and words_preferred files contain zeta values(?) rather than words. But that's too complicated for me to fix right now. 

I don't read my Huygens mail at the moment, but I do follow pboot@xs4all.nl.

Best,
Peter