cli tool: do not use disabled protocols

cli tool: do not use disabled protocols

As they are now rejected by the library, take care of not passing
disabled protocol names to CURLOPT_PROTOCOLS_STR and
CURLOPT_REDIR_PROTOCOLS_STR.

Rather than using the CURLPROTO_* constants, dynamically assign protocol
numbers based on the order they are listed by curl_version_info().

New type proto_set_t implements prototype bit masks: it should therefore
be large enough to accomodate all library-enabled protocols. If not,
protocol numbers beyond the bit count of proto_set_t are recognized but
"inaccessible": when used, a warning is displayed and the value is
ignored. Should proto_set_t overflows, enabled protocols are reordered to
force those having a public CURLPROTO_* representation to be accessible.

Code has been added to subordinate RTMP?* protocols to the presence of
RTMP in the enabled protocol list, being returned by curl_version_info()
or not.