In evarconv and unification, expand folded primitive projections to
their eta-expanded forms which can then unfold back to the unfolded
primitive projection form. This removes all special code that
was necessary to handle primitive projections before, while keeping
compatibility.
Also fix cbn which was not refolding primitive projections correctly
in all cases.
Update some test-suite files accordingly.
Fix printing of primitive record info.
Fix test-suite files

3566 gave a legitimate error, keyedrewrite was not setting keyed
unification on.
Bug fixed.
Adding a test for bug #2428.