Coverity issue 1187618. Double close. Fixed a problem in

 obit_reply where the socket connection was getting closed
 twice. The tricky part on this was that we used the cnt2server
 API to open the connection and then used add_conn to add the
 obit_reply as the function handler to the socket for the
 internal table. To be consistent we call pbs_disconnect_socket
 but cannot call close_conn because we have already closed
 the socket. I added a new function, clear_conn which does
 everything that close_conn does except call any exit routines
 and close the socket