Try to close server during shutdown

If the server never accepts a client, joining on this thread will
hang the spec and never be terminated because it happens in an
"after" section. Instead, we try to close the server if it has not
already been closed, so it will terminate gracefully.

See #925

library/socket/fixtures/classes.rb

@@ -118,14 +118,14 @@ def service(socket)
 
         socket.send data, 0
       ensure
-        socket.close
+        socket.close unless socket.closed?
       end
     end
 
     def shutdown
       log "SpecTCPServer shutting down"
+      @server.close unless @server.closed?
       @thread.join
-      @server.close
     end
 
     def log(message)

library/socket/udpsocket/send_spec.rb

@@ -16,13 +16,14 @@
           retry
         end
       ensure
-        @server.close if !@server.closed?
+        @server.close unless @server.closed?
       end
     end
     Thread.pass while @server_thread.status and !@port
   end
 
   after :each do
+    @server.close unless @server.closed?
     @server_thread.join
   end