SSL: Add an option to disable certificate revocation checks

New tool option --ssl-no-revoke.
New value CURLSSLOPT_NO_REVOKE for CURLOPT_SSL_OPTIONS.

Currently this option applies only to WinSSL where we have automatic
certificate revocation checking by default. According to the
ssl-compared chart there are other backends that have automatic checking
(NSS, wolfSSL and DarwinSSL) so we could possibly accommodate them at
some later point.

Bug: https://github.com/bagder/curl/issues/264


Reported-by: zenden2k <zenden2k@gmail.com>