print_hoa: diagnose unknown options

* src/twaalgos/hoa.cc: Here.
* src/tests/readsave.test: Test it.
* NEWS: Mention it.
* src/twaalgos/dot.cc, src/twaalgos/neverclaim.cc: Fix the
error message.

src/tests/readsave.test

@@ -696,3 +696,7 @@ State: 2
 EOF
 
 diff output3 expect3
+
+
+$autfilt -Hk input 2>stderr && exit 1
+grep 'print_hoa.*k' stderr

src/twaalgos/dot.cc

@@ -173,7 +173,7 @@ namespace spot
 	      break;
 	    default:
 	      throw std::runtime_error
-		(std::string("unknown option for dotty(): ") + c);
+		(std::string("unknown option for print_dot(): ") + c);
 	    }
       }
 

src/twaalgos/hoa.cc

@@ -247,7 +247,7 @@ namespace spot
     if (opt)
       while (*opt)
 	{
-	  switch (*opt++)
+	  switch (char c = *opt++)
 	    {
 	    case 'i':
 	      implicit_labels = true;
@@ -264,6 +264,9 @@ namespace spot
 	    case 't':
 	      acceptance = Hoa_Acceptance_Transitions;
 	      break;
+	    default:
+	      throw std::runtime_error
+		(std::string("unknown option for print_hoa(): ") + c);
 	    }
 	}
 

src/twaalgos/neverclaim.cc

@@ -61,7 +61,8 @@ namespace spot
 		break;
 	      default:
 		throw std::runtime_error
-		  (std::string("unknown option for never_claim(): ") + c);
+		  (std::string("unknown option for print_never_claim(): ")
+		   + c);
 	      }
       }