[SceneLoader] Add a special error message handler for DeprecationWarning (#384)

* [SofaPython3/Plugin] Add a special error message handler for DeprecationWarning

Otherwise deprecation messages appears as error which is misleading for users.

* Update Plugin/src/SofaPython3/SceneLoaderPY3.cpp

Co-authored-by: Alex Bilger <alxbilger@users.noreply.github.com>

---------

Co-authored-by: Alex Bilger <alxbilger@users.noreply.github.com>

Author: damienmarchal

Plugin/src/SofaPython3/SceneLoaderPY3.cpp

@@ -129,9 +129,18 @@ void SceneLoaderPY3::loadSceneWithArguments(const char *filename,
         root_out->setInstanciationSourceFilePos(0);
     }catch(py::error_already_set& e)
     {
-        msg_error() << "Unable to completely load the scene from file '"<< filename << "'." << msgendl
-                    << "Python exception: " << msgendl
-                    << "  " << e.what();
+        std::stringstream ss;
+        ss << "Unable to completely load the scene from file '"<< filename << "'." << msgendl
+            << "Python exception: " << msgendl
+            << "  " << e.what();
+        if( py::isinstance(e.type(), py::eval("type(DeprecationWarning)")) )
+        {
+            msg_deprecated() << ss.str();
+        }else
+        {
+            msg_error() << ss.str();
+        }
+
     }
 
 }