tests: do not catch polymorphic type by value

dune/tnnmg/test/multitypegstest.cc

@@ -256,7 +256,7 @@ int main(int argc, char** argv) try
 
   return passed ? 0 : 1;
 }
-catch (Dune::Exception e) {
+catch (const Dune::Exception& e) {
 
     std::cout << e << std::endl;
 

dune/tnnmg/test/nonlineargsperformancetest.cc

@@ -278,7 +278,7 @@ int main(int argc, char** argv) try
 
     return passed ? 0 : 1;
 }
-catch (Dune::Exception e) {
+catch (const Dune::Exception& e) {
 
     std::cout << e << std::endl;
 

dune/tnnmg/test/nonlineargstest.cc

@@ -354,7 +354,7 @@ int main(int argc, char** argv) try
 
     return passed ? 0 : 1;
 }
-catch (Dune::Exception e) {
+catch (const Dune::Exception& e) {
 
     std::cout << e << std::endl;
 

dune/tnnmg/test/simplexsolvertest.cc

@@ -91,7 +91,7 @@ int main(int argc, char** argv) try {
       try {
         solver(x, f, ignore);
         passed = passed and false;
-      } catch (Dune::NotImplemented) {
+      } catch (const Dune::NotImplemented&) {
         passed = passed and true;
       }
       ignore[0] = false;
@@ -181,6 +181,6 @@ int main(int argc, char** argv) try {
   }
 
   return passed ? 0 : 1;
-} catch (Dune::Exception e) {
+} catch (const Dune::Exception& e) {
   std::cout << e << std::endl;
 }

dune/tnnmg/test/tnnmgsteptest.cc

@@ -263,7 +263,7 @@ int main(int argc, char** argv) try
 
     return suite.exit();
 }
-catch (Dune::Exception e) {
+catch (const Dune::Exception& e) {
 
     std::cout << e << std::endl;