fix timeout by checking the socket for errors

Mart Lubbers
2019-10-03T16:56:00+02:00

In the old situation when the connect didn't immediately return, the
socket was placed in a select.
An error was throws only when the socket was in the exceptset. However,
sockets are only in the exceptset in very particular cases (see man
select). Unable to connect is not one of those cases.

Therefore to actually check if a connection was refused, the error
status must be checked with getsockopt.

Also see (https://stackoverflow.com/questions/2597608/c-socket-connection-timeout/2597774#2597774)

Closes: clean-and-itasks/iTasks-SDK#348