Preliminary work-around to only substitute by any/empty variables that were introduced by the tallying.

of sequence|non_variable|(toplevelvar ^ rest)
with special cases when non_variable or sequence are empty and toplevelvar or rest are any
(or any combination of thoses).

Add the examples of the part2 paper in a test file.

- delta is not yet used to do anything meaningful
- remove optional argument ?fresh from Var.mk (legacy not used)
- print -> pp,printf refactoring

Conflicts:
	types/var.ml

- fix one more problem with internalize
- fix variance/contravariance problem in substituterec
- cleanup

- performance improvements (add memoization)
- fix infinite loops due to recursive structures
- add apply tests (kim)

Tallying.CS.cup -> union
Tallying.CS.cap -> prod

lessgeneral m1 m2 check if the constraint set m1 is less general of m2

- type variables are now correctly parsed as patterns
  and not as expressions

- Add a new module Var that contains all the type variables
  related machinery

- Remove old functions and unit tests about BoolVar of only
  variables, since now variables are always stored associated
  with one or more kinds