- 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

now as such:
	- ['a] is the regexp matching the type variable "a";
	- ['a'] is the regexp matching the string "a";
	- ['a' 'a] is the regexp matching the string "a" followed by the type
	variable "a";
	- ['a''a] is a syntax error (a string in single quotes in a regexp MUST
	be followed by a character that cannot be the beginning of a name for a
	type variable, a blank character will do).

Bug: At this point, when using CDuce at toplevel, one will have to press enter
twice when typing a regexp with type variables.

[TESTS] Add functions nth and rev and tests for stdlib/list

Fix tests of ocaml interface