Use the length operator (#) instead of table.getn.

table.getn was deprecated in Lua 5.1 in favor of #, the length operator.
See: http://www.lua.org/manual/5.1/manual.html#7.2

etc/check-links.lua

@@ -11,7 +11,7 @@ dispatch.TIMEOUT = 10
 
 -- make sure the user knows how to invoke us
 arg = arg or {}
-if table.getn(arg) < 1 then
+if #arg < 1 then
     print("Usage:\n  luasocket check-links.lua [-n] {<url>}")
     exit()
 end