python: fix output of twa_run

* src/twaalgos/emptiness.hh, src/twaalgos/emptiness.cc: Declare the
operator<< for twa_run, not for twa_run_ptr (the shared_ptr
automatically forward operator<<).
* wrap/python/spot_impl.i: Add __str__ to twa_run, not twa_run_ptr.

src/twaalgos/emptiness.cc

@@ -254,9 +254,9 @@ namespace spot
   }
 
   std::ostream&
-  operator<<(std::ostream& os, const twa_run_ptr& run)
+  operator<<(std::ostream& os, const twa_run& run)
   {
-    auto& a = run->aut;
+    auto& a = run.aut;
     bdd_dict_ptr d = a->get_dict();
 
     auto pstep = [&](const twa_run::step& st)
@@ -268,11 +268,11 @@ namespace spot
       os << '\n';
     };
 
-    os << "Prefix:" << std::endl;
-    for (auto& s: run->prefix)
+    os << "Prefix:\n";
+    for (auto& s: run.prefix)
       pstep(s);
-    os << "Cycle:" << std::endl;
-    for (auto& s: run->cycle)
+    os << "Cycle:\n";
+    for (auto& s: run.cycle)
       pstep(s);
     return os;
   }

src/twaalgos/emptiness.hh

@@ -332,7 +332,7 @@ namespace spot
     /// actually exists in the automaton (and will also display any
     /// transition annotation).
     SPOT_API
-    friend std::ostream& operator<<(std::ostream& os, const twa_run_ptr& run);
+    friend std::ostream& operator<<(std::ostream& os, const twa_run& run);
   };
   /// @}
 

wrap/python/spot_impl.i

@@ -383,7 +383,7 @@ namespace std {
   }
 }
 
-%extend spot::twa_run_ptr {
+%extend spot::twa_run {
   std::string __str__()
   {
     std::ostringstream os;