Add. Allow get error option to socket.

test/test_socket_error.lua

@@ -0,0 +1,27 @@
+local socket = require "socket"
+
+local host, port = "127.0.0.1", "5462"
+
+assert(socket.bind(host, port)):close()
+
+local sock = socket.tcp()
+sock:settimeout(0)
+
+local ok, err = sock:connect(host, port)
+assert(not ok)
+assert('timeout' == err)
+
+for i = 1, 10 do
+  -- select pass even if socket has error
+  local _, rec, err = socket.select(nil, {sock}, 1)
+  assert('timeout' == err)
+  assert(not next(rec))
+  err = sock:getoption("error") -- i get 'connection refused' on WinXP
+  if err then
+    print("Passed! Error is '" .. err .. "'.")
+    os.exit(0)
+  end
+end
+
+print("Fail! No error detected!")
+os.exit(1)