Get MPlambdaTheory to build again.

Extract a usable half-way point from nominal_datatype branch.

This replaces the is_perm predicate with a type embodying that predicate.
It doesn't include the subsequent work on allowing multiple 'atom' types.

Rework lambda-theory scripts to use new varying parameter recursion theorem.

Also make work for myself by having some of the script files use
'tight' equality. Later files get switched back to loose (prec = 100)
equality, because it was all getting to be too much work.

Removed trailing whitespace from all .sml and .sig files.

This affects over 900 files and was done using emacs's delete-trailing-whitespace
function in batch mode. Building the system with Poly/ML and Moscow ML seems to
work, so I'm hoping these changes don't break anything. Please complain if
they do!

Fixes for these examples, and an updated MANIFEST/README in
other-models. The other-models directory had become particularly
stale. I obviously need to check that it works more often. (Main
problem: change to behaviour of Q.INST.)

A whole mess of small changes intended
at making simpsets prettyprint informatively
in the interactive loop. Very possibly
I haven't updated all the files in the examples
directories.

Completely reorganise these files into some sensible directories.
Also, add a file demonstrating that the McKinna-Pollack two-sorted raw
syntax does indeed behave properly (links appropriately to beta over
quotiented terms).