Introduce Win32 AcceptFilter handling.

Divided into 3 classes, this implements the first two;

 * AcceptFilter 'data' - much as on Unix, accept will not complete
   until data is ready to be accepted.  Unlike Unix, it will actually
   fetch the first bucket full of data from the tcp socket, and this
   patch implements passing that bucket into the core net brigade
   in front of the accepted socket.

 * AcceptFilter 'connect' - just as in Apache 2.2, accept will not
   complete until three way handshake is complete and the endpoints
   are resolved, and quickly grabs the endpoint addresses using the
   AcceptEx API (which some people have problems with).  This will
   not be the default.

 * AcceptFilter 'none' [not yet implemented] - will be the traditional
   select/WSAAccept style processing for broken network socket stacks
   and more trivial tcp style connections.  If AcceptEx appears to be
   a problem, the listener will be able to downgrade to 'none'.



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@735093 13f79535-47bb-0310-9956-ffa450edef68