Added a test case for rudel-server to rudel-connections.el
* rudel-connections.el
  (rudel-connections-test-server->client-connection): new class; work
  around abstractness of `rudel-server->client-connection' for tests
  (rudel-connections-test-server): new class; work around abstractness
  of `rudel-server' for tests
  (rudel-connections-test-server-object-print): new test; test for
  `object-print' method of `rudel-server'