simplifier: new LTL simplifications

if e is pure eventuality and g => e, then e U g = Fg
if u is purely universal and u => g, then u R g = Gg

Fixes #93.

* doc/tl/tl.tex, NEWS: Document the rules.
* spot/tl/simplify.cc: Implement them.
* tests/core/reduccmp.test: Test them.
* tests/core/det.test: Adjust.

tests/core/reduccmp.test

@@ -1,6 +1,6 @@
 #! /bin/sh
 # -*- coding: utf-8 -*-
-# Copyright (C) 2009, 2010, 2011, 2012, 2013, 2014 Laboratoire de
+# Copyright (C) 2009, 2010, 2011, 2012, 2013, 2014, 2016 Laboratoire de
 # Recherche et Developpement de l'Epita (LRDE).
 # Copyright (C) 2004, 2006 Laboratoire d'Informatique de Paris 6 (LIP6),
 # département Systèmes Répartis Coopératifs (SRC), Université Pierre
@@ -104,6 +104,16 @@ b U GFa, GFa
 Ga, Ga
 
 a U XXXFb, XXXFb
+
+# issue 93
+GFa U Ga, FGa
+FGa U Ga, FGa
+GFa U a, GFa U a
+Fa U a, Fa
+GFa R Fa, GFa
+FGa R Fa, GFa
+FGa R a, FGa R a
+Ga R a, Ga
 EOF
 
 cp common.txt nottau.txt