allow specifying a fixed seed in the config file for generating the map (fixed_map_seed)

src/defaultsettings.cpp

@@ -85,6 +85,7 @@ void set_default_settings()
 	g_settings.setDefault("default_privs", "build, shout");
 	g_settings.setDefault("profiler_print_interval", "0");
 	g_settings.setDefault("enable_mapgen_debug_info", "false");
+	g_settings.setDefault("fixed_map_seed", "");
 
 	g_settings.setDefault("objectdata_interval", "0.2");
 	g_settings.setDefault("active_object_range", "2");

src/map.cpp

@@ -1879,10 +1879,17 @@ ServerMap::ServerMap(std::string savedir):
 
 	//m_chunksize = 8; // Takes a few seconds
 
-	m_seed = (((u64)(myrand()%0xffff)<<0)
+	if (g_settings.get("fixed_map_seed").empty())
-			+ ((u64)(myrand()%0xffff)<<16)
+	{
-			+ ((u64)(myrand()%0xffff)<<32)
+		m_seed = (((u64)(myrand()%0xffff)<<0)
-			+ ((u64)(myrand()%0xffff)<<48));
+				+ ((u64)(myrand()%0xffff)<<16)
+				+ ((u64)(myrand()%0xffff)<<32)
+				+ ((u64)(myrand()%0xffff)<<48));
+	}
+	else
+	{
+		m_seed = g_settings.getU64("fixed_map_seed");
+	}
 
 	/*
 		Experimental and debug stuff