Begin to abstract out the underlying transport layer.

The first step is to remove the socket from the conn_rec,
the server now lives in a context that is passed to the
core's input and output filters. This forces us to be very
careful when adding calls that use the socket directly,
because the socket isn't available in most locations.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@91887 13f79535-47bb-0310-9956-ffa450edef68