Function Curl_socket_check

* Wait for read or write events on a set of file descriptors. It uses poll() * when poll() is available, in order to avoid limits with FD_SETSIZE, * otherwise select() is used. An error is returned if select() is being used * and a file descriptor is too large for FD_SETSIZE. * * A negative timeout value makes this function wait indefinitely, unless no * valid file descriptor is given, when