cancel threads instead of waiting for join

[Ckath]

currently, whenever an error about the port being in use or being unable to setup the server comes out of accept_thread(&ainfo);, the server will still merrily go along and let all the threads run indefinitely until I manually ^C it. with pthread_cancel instead of pthread_join they get canceled and it can actually exit if accept_thread(&ainfo); were to return prematurely.