Inspired by #17, compared our Nitfol source to the source from its last

Inspired by #17, compared our Nitfol source to the source from its last
stable release (0.5) and reduced the changes to a minimum. Some useful
patches seem to have been applied in Gargoyle, which I have kept. All the
changes are in a file 'interpreters/nitfol.patch' for future reference.

Glk Frotz doesn't exist anywhere outside of Gargoyle, so I have made it
exactly equal to r268 of the Gargoyle source.

git-svn-id: http://lassie.dyndns-server.com/svn/gargoyle-gtk@113 ddfedd41-794f-dd11-ae45-00112f111e67