Introduce spot::state_set.

* src/tgba/state.hh: Define state_set and shared_state_set.
* src/tgba/taatgba.cc, src/tgba/taatgba.hh: Rename the existing
state_set (that inherits from spot::state) as set_state.
* src/tgba/tgbakvcomplement.cc: Use shared_state_set instead
of state_set.
* src/tgbaalgos/minimize.cc (state_set): Rename as...
(build_state_set): ... this.

src/tgba/state.hh

@@ -30,6 +30,7 @@
 #include <functional>
 #include <boost/shared_ptr.hpp>
 #include "misc/casts.hh"
+#include "misc/hash.hh"
 
 namespace spot
 {
@@ -171,6 +172,11 @@ namespace spot
     }
   };
 
+  typedef Sgi::hash_set<const state*,
+			spot::state_ptr_hash,
+			spot::state_ptr_equal> state_set;
+
+
   // Functions related to shared_ptr.
   //////////////////////////////////////////////////
 
@@ -259,6 +265,10 @@ namespace spot
     }
   };
 
+  typedef Sgi::hash_set<shared_state,
+			state_shared_ptr_hash,
+			state_shared_ptr_equal> shared_state_set;
+
 }
 
 #endif // SPOT_TGBA_STATE_HH