Make the organsiation of the mllex source-code a bit cleaner so that
the polyml version can be built more easily. If you have polyml
installed nicely, it should be possible to get a poly version of mllex
by just going
make -f Holmakefile mllex.exe
in the tools/mllex directory. The tricksiness in Holmakefile is more
cute than useful, as it's not used by Holmake.