http: Add reference counting to the session object.
* common/http.c (http_session_t): Add field "refcount". (_my_socket_new, _my_socket_ref, _my_socket_unref): Add debug code. (send_request, my_npth_read, my_npth_write): Use SOCK object for the transport ptr. (http_session_release): Factor all code out to ... (session_unref): here. Deref SOCK. (http_session_new): Init refcount and transport ptr. (http_session_ref): New. Ref and unref all assignments.
Having the reference counted session objects makes it easier for the
application to pass around only an estream. Without that the
application would need to implement an es_onclose machinery for the
session object.