Update solitaire_s.c

Attempted to multithread solitaire code using Jim's examples of echoclient and server. Changes mostly in main; added a listening loop that makes new connections; increased number of MAXCONNECTIONS; made new struct type _client_t; changed arg type of playSolitaire to void * in order to pass it to new threads. playSolitaire is analogous to the proc echo_session in the echoserver code.