Improve the debugging of the unify step of the tallying. Fix a bug where substitutions were applied in the wrong order, yielding partially empty types.

Refactor the Bool/BoolVar code so that they share the same interface. Give access to the underlying atom module in BoolVar.

Improve pretty printing of Bdds and add debug directive to interactively inspect the internal representation of types.

Add a workaround in case pattern compilation failed (after typechecking) due to the presence of type variables in some types.

This reverts commit a8ba6ab6.

This commit introduces a regression where suprious type variables are introduced in the final type.

Perform a more aggressive memoization of substituted types and register the name if the original type was named.
Make the pretty-printer re-entrant.

- type t 'a = ('a,'a)
- type t ('a,'b) = ('a,'b)

Fix Typer.pp_env printer for types
Minor code refactring

Conflicts:
	Makefile.distrib
	depend

Change $$ in >> in types.ml for the substitution operator

Do not generate equations for monomorphic variables, during the generation of type equation from constraints.

- delta is now kept into consideration when memoizing

Tallying and printing still broken.

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

- from Module.xxx_to_string to Module.Print.string_of_xxxx
- from Module.print_xxx to Module.Print.pp_xx

- refactoring in types.ml
- add Types.squareapply
- other fixes

- refactoring in types.ml
- add Types.squareapply
- other fixes

- Add delta as optional parameter to Tallying.talling.
- Add (++) product of two lazy types substitutions.
- Add (@@) application of a lazy type substition to a type.
- Add ($$) application of a explicit type substution to a type.