Merge prusa 2.6.1

src/libslic3r/Config.hpp

@@ -2160,6 +2160,10 @@ protected:
     // If the opt_key is no more valid in this version of Slic3r, opt_key is cleared by handle_legacy().
     // handle_legacy() is called internally by set_deserialize().
     virtual void                    handle_legacy(t_config_option_key &/*opt_key*/, std::string &/*value*/) const {}
+    // Called after a config is loaded as a whole.
+    // Perform composite conversions, for example merging multiple keys into one key.
+    // For conversion of single options, the handle_legacy() method above is called.
+    virtual void                    handle_legacy_composite() {}
 
 public:
 	using ConfigOptionResolver::option;