protocols: use CURLPROTO_ internally

The PROT_* set of internal defines for the protocols is no longer
used. We now use the same bits internally as we have defined in the
public header using the CURLPROTO_ prefix. This is for simplicity and
because the PROT_* prefix was already used duplicated internally for a
set of KRB4 values.

The PROTOPT_* defines were moved up to just below the struct definition
within which they are used.

lib/file.c

@@ -127,7 +127,7 @@ const struct Curl_handler Curl_handler_file = {
   ZERO_NULL,                            /* perform_getsock */
   ZERO_NULL,                            /* disconnect */
   0,                                    /* defport */
-  PROT_FILE,                            /* protocol */
+  CURLPROTO_FILE,                       /* protocol */
   PROTOPT_BANPROXY                      /* flags */
 };