This is suggested by the paper. By default any uninferred type will
cause a compilation error. If this boolean is set to true, any
uninstantiated type will be defaulted to Type.Int.

Used `=` instead of `<>` when checking if id does NOT occur...

Revert ack.ml test to use smaller values.

Modified description of prog_of_knorm in closure.ml comment, and added mli files for closure/constant.ml

Due to inline-expansion (see dfc9fea9) every variable binding is assigned
a new id. So there is no longer need for the function new_name.

Before this the alpha-conversion would leave variable-names alone if
they were the first occurence (in the let case). However, when a
function was inlined multiple times this would cause duplicate varaible
defintions subverting the purpose of alpha-conversion.

Not refactored yet.