add some strategic lua gc steps.

gtk2_ardour/luainstance.cc

@@ -1147,6 +1147,7 @@ LuaInstance::call_action (const int id)
 {
 	try {
 		(*_lua_call_action)(id + 1);
+		lua.collect_garbage_step ();
 	} catch (luabridge::LuaException const& e) {
 		cerr << "LuaException:" << e.what () << endl;
 	}

gtk2_ardour/processor_box.cc

@@ -1723,6 +1723,7 @@ ProcessorEntry::LuaPluginDisplay::render_inline (cairo_t *cr, uint32_t width)
 	Cairo::Context ctx (cr);
 	try {
 		luabridge::LuaRef rv = (*_lua_render_inline)((Cairo::Context *)&ctx, width, _max_height);
+		lua_gui.collect_garbage_step ();
 		if (rv.isTable ()) {
 			uint32_t h = rv[2];
 			return h;