Add insecure SSL transfer support.

This adds a new option that acts in the same manner as curl's --insecure
option. The flags '-i' and '--insecure' activate this option.

From the curl(1) manpage:
> (SSL) This option explicitly allows curl to perform "insecure" SSL
> connections and transfers. All SSL connections  are attempted  to  be
> made secure by using the CA certificate bundle installed by default.
> This makes all connections considered "insecure" fail unless -k,
> --insecure is used.