Area-based MapEditEvent ignore and that put to use for on_generate too

src/server.h

@@ -823,6 +823,13 @@ private:
 		This is behind m_env_mutex
 	*/
 	bool m_ignore_map_edit_events;
+	/*
+		If a non-empty area, map edit events contained within are left
+		unsent. Done at map generation time to speed up editing of the
+		generated area, as it will be sent anyway.
+		This is behind m_env_mutex
+	*/
+	VoxelArea m_ignore_map_edit_events_area;
 	/*
 		If set to !=0, the incoming MapEditEvents are modified to have
 		this peed id as the disabled recipient