warn instead of error for multi-step MED meshes

Geo/GModelIO_MED.cpp

@@ -261,7 +261,7 @@ int GModel::readMED(const std::string &name, int meshIndex)
   // e.g. meshName_step%d). This way we could also handle multi-mesh
   // time sequences in MED3.
   if(nStep > 1)
-    Msg::Error("Discarding %d last meshes in multi-step MED mesh", nStep - 1);
+    Msg::Warning("Discarding %d last meshes in multi-step MED mesh", nStep - 1);
 
   setName(meshName);
   if(meshType == MED_NON_STRUCTURE){