make :members() not return index, add -DBLLUA_ALLOWFFI, allow reading modules/lualib/, bug fixes

src/lua-env.lua

@@ -37,5 +37,9 @@ function _bllua_on_error(err)
 	return table.concat(tracelines, '\n')
 end
 
+-- overridden in lua-env-safe.lua (executed if not BLLUA_UNSAFE)
+_bllua_io_open = io.open
+_bllua_requiresecure = require
+
 print = _bllua_ts.echo
 print('  Executed bllua-env.lua')