Settings: pass name to callbacks by reference

Spare some copies.

src/clouds.cpp

@@ -30,7 +30,7 @@ class Clouds;
 Clouds *g_menuclouds = NULL;
 irr::scene::ISceneManager *g_menucloudsmgr = NULL;
 
-static void cloud_3d_setting_changed(const std::string settingname, void *data)
+static void cloud_3d_setting_changed(const std::string &settingname, void *data)
 {
 	((Clouds *)data)->readSettings();
 }

src/fontengine.cpp

@@ -35,7 +35,8 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 FontEngine* g_fontengine = NULL;
 
 /** callback to be used on change of font size setting */
-static void font_setting_changed(const std::string, void *userdata) {
+static void font_setting_changed(const std::string &name, void *userdata)
+{
 	g_fontengine->readSettings();
 }
 

src/game.cpp

@@ -806,7 +806,7 @@ class GameGlobalShaderConstantSetter : public IShaderConstantSetter
 			m_fogEnabled = g_settings->getBool("enable_fog");
 	}
 
-	static void SettingsCallback(const std::string name, void *userdata)
+	static void SettingsCallback(const std::string &name, void *userdata)
 	{
 		reinterpret_cast<GameGlobalShaderConstantSetter*>(userdata)->onSettingsChange(name);
 	}

src/settings.h

@@ -36,7 +36,7 @@ extern Settings *g_settings;
 extern std::string g_settings_path;
 
 /** function type to register a changed callback */
-typedef void (*setting_changed_callback)(const std::string, void*);
+typedef void (*setting_changed_callback)(const std::string &name, void *data);
 
 enum ValueType {
 	VALUETYPE_STRING,