Add alternative is_socket_connected implementation.

It works on win32 and linux for sure, so that's why
I put it inside the #ifdef.
Of course something like that needs APR abstraction.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@451580 13f79535-47bb-0310-9956-ffa450edef68