New function: client_sock_fd(). It returns the socket fd used

New function: client_sock_fd().  It returns the socket fd used
by the transport_session underlying a specified transport_client.

Purpose: increase the level of encapsulation, so that the
calling code doesn't need to know about three layers of internals.

M    include/opensrf/transport_client.h
M    src/libopensrf/transport_client.c

git-svn-id: svn://svn.open-ils.org/OpenSRF/trunk@1837 9efc2488-bf62-4759-914b-345cdb29e865