7.0 -> 7.1 : mostly bug corrections. No theoretical problems dealed with.

* The semantics of Extract Constant changed: If you provide a extraction 
for p by Extract Constant p => "0", your generated ML file will begin by 
a let p = 0. The old semantics, which was to replace p everywhere by the
provided terms, is still available via the Extract Inlined Constant p => 
"0" syntax.


* There are more optimizations applied to the generated code: 
- identity cases: match e with P x y -> P x y | Q z -> Q z | ...
is simplified into e. Especially interesting with the sumbool terms: 
there will be no more match ... with Left -> Left | Right -> Right

- constant cases: match e with P x y -> c | Q z -> c | ...
is simplified into c as soon as x, y, z do not occur in c.
So no more match ... with Left -> Left | Right -> Left.
  

* the extraction at Toplevel (Extraction foo and Recursive Extraction foo),
which was only a development tool at the beginning, is now closer to 
the real extraction to a file. In particular optimizations are done, 
and constants like recursors ( ..._rec ) are expanded. 


* the singleton optimization is now protected against circular type.
( Remind : this optimization is the one that simplify 
type 'a sig = Exists of 'a  into type 'a sig = 'a and 
match e with (Exists c) -> d into let c = e in d ) 


* Fixed one bug concerning casted code


* The inductives generated should now have always correct type-var list 
('a,'b,'c...)


* Code cleanup until three days before release. Messing-up code 
in the last three days before release.







6.x -> 7.0 : Everything changed. See README