Remove some old cruft.
Partial conversion to class scored_combo_tree

The nested pairs of pairs of pairs has gotten very challenging to
debug (never mind read and understand, for newcomers)  Start fixing
this.
Ongoing refactoring of the scored tree system.

The code still doesn't compile. But we're getting closer...
Ongoing refactoring of the scored tree system.

All code compiles, one unit test fails.
Fix combo tree hashing function
Merge pull request #790 from linas/clust

MOSES: rework the scoring infrastructure.