Only actually needed servers should be listed and none is then implied
if no servers are listed.
Outputs a warning if "none" is still set as a server.
Closes#18466
This commit adds curl_multi_wakeup() which was previously in the TODO
list under the curl_multi_unblock name.
On some platforms and with some configurations this feature might not be
available or can fail, in these cases a new error code
(CURLM_WAKEUP_FAILURE) is returned from curl_multi_wakeup().
Fixes#4418Closes#4608
