Passing a void pointer is unsafe.

Allows the kernel to combine timer wakeups with other processes,
reducing power usage.

Make it "const".

Another big chunk of code for multi-player support.

.. and move the plugins to src/encoder/plugins/.

Users now have to call Close() explicitly.  This simplifies using the
class, as most users have automatic socket management already, and
Steal() had to be used often.

This call is not thread-safe.

Fixes more thread-safety bugs.

Add a Page queue to class HttpdOutput, and use DeferredMonitor to
flush this queue inside the IOThread.  This fixes a thread-safety
issue: much of EventLoop is not thread-safe, and the httpd plugin
ignored that problem.

Do all I/O in the IOThread and not in the main thread.  This solves an
upcoming deadlock problem.

Don't let the server care for client problems.

Don't iterate the std::list each time.