Function add_next_timeout

* add_next_timeout() * * Each Curl_easy has a list of timeouts. The add_next_timeout() is called * when it has been removed from the splay tree because the timeout has * expired. This function is then to advance in the list to pick the next * timeout to use (skip the already expired ones) and add this node back to * the splay tree again. * * The splay tree only has each sessionhandle as a