Further simplify the type algebra code, using the newly introduced combinators (map/fold/iter) over types.

Move the bool.ml{,i} files in types/ where they belong.

Add more test cases to the the pretty printer/parser test suite.

Fix various bugs in the pretty-printer (union of atoms not parenthesized, | instead of & for some toplevel variables)

Add a wrapper around the type printing function to prevent them from outputing illegal code (such as [(Char | (*--2)*)* ]. (which contains CDuce comments).

Implement some semantic simplification of BDDs. This fixes the exponential beahviour during the typing of the application of flatten.

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.

exponentially large types in some cases. This simplifies types of the form:
T & 'a | T \ 'a into T.

because they appeared both on negative and positive occurences in bdds
that are equivalent to the empty type.

For instance t = ('a | (Int\'a) | Int)

We use product normalization to clean up this.

Use the new debugging infrastructure to see what is going on during constraint solving.

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

Fix a stupid typo which made the constraint solver prefer monomorphic variables over polymorphic ones.
This prevented one from applying a polymorphic function in the body of another function.

Make it so that the substitution function preserves as much sharing as possible from the original type.

This reverts commit a8ba6ab6.

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

Seal the representation of SortedList.Make(X).t (by making the type private). Expose Var.Set as a SortedList.S