This reverts commit f56c6a18.  This
fix is not necessary anymore because clients are now being deleted by
the timer callback.

Don't use a global loop over the whole client list.

Fixes assertion failure (regression).

Allow creating a closed SocketMonitor instance.

Use WinSock errors on Windows.

Make a class that contains the formatting code and the buffer.

Using initializer list.

Not necessary, GLib will pick up the updated GPollFD automatically.

.. instead of calling g_main_loop_quit(), which may dead-lock.