Async send

[Bill Stoddard <bi...@wstoddard.com>]

In case anyone is interested... I am spending my development time on getting
the Windows MPM to do asynchronous network sends.  I have working code to
handle non-keep alive connections.  In basically exploratory mode now trying
to understand the key design points and issues. Working on send rather than
receive because I believe that is where the big win is.  We can already
control how long we block on reads with keepalivetimeout. We cannot control
how long it takes to do sends.

 My goals are:

1. Get async send working for non-keep alive connections
Done

2. Extend to get async send working for keep-alive connections
Should provide some experience with setting async call-back routines that
should be called when an async i/o event triggers. Also provide insite to
Apache design changes necessary to handle async i/o.

3. Compare the Windows solution comptability with the BSD Kqueue/Kevent API

4. Attempt to create a unified API (that can be implemented in OS specific
ways, such as iocompletionports, Kqueue/Kevent, etc)

5. Push network i/o event handling infrastructure into APR

Bill