Nary unification now uses Sequence (simpler, more efficient)
unif.res_head
refactor: unification now works with two (optional) DB environments
in which bound variables of both terms live.
matching: parameter ?allow_open is now used properly in rewriting and indexing
target in Makefile to update @next_release tags
arith binary predicates are polymorphic
oasis: --demo flag, to enable src/demo/ demonstration programs;
small resolution prover for didactic purpose added in src/demo/resolution
small change in _oasis about doc
move the demo program resolution.ml into resolution1.ml;
build its documentation (wip, need to keep code and all that)
merge from dev
release 0.5.2