Make it possible to output UTF-8 for dotty().

* src/tgba/tgbaexplicit.hh: Rerganize a bit to
allow different functions to be used to format
states.  Add an enabled_utf8() method to
tgba_explicit_formula.
* src/tgbaalgos/dotty.hh, src/tgbaalgos/dotty.cc:
Simplify the interface by not depending on
dotty_decorator explicitely.
* src/tgba/bddprint.hh (enable_utf8): New function.
* src/tgba/bddprint.cc (enable_utf8): Implement it
and use the global utf8 flag in other functions.
* src/tgbatest/ltl2tgba.cc: Add an -8 option for
UTF-8 outpout.
* wrap/python/spot.i: Adjust for tgbexplicit.hh
changes.

src/tgba/bddprint.hh

@@ -1,4 +1,4 @@
-// Copyright (C) 2003, 2004  Laboratoire d'Informatique de Paris 6 (LIP6),
+// Copyright (C) 2003, 2004, 2012  Laboratoire d'Informatique de Paris 6 (LIP6),
 // département Systèmes Répartis Coopératifs (SRC), Université Pierre
 // et Marie Curie.
 //
@@ -113,6 +113,8 @@ namespace spot
   std::ostream& bdd_print_table(std::ostream& os,
 				const bdd_dict* dict, bdd b);
 
+  /// \brief Enable UTF-8 output for bdd printers.
+  void enable_utf8();
 }
 
 #endif // SPOT_TGBA_BDDPRINT_HH