Update net/ddclient to 3.9.1

Hi,

I've attached a small patch to update ddclient from 3.8.3 to 3.9.1. The project has moved to GitHub (as noted on the old sourceforge homepage) and the dependencies have changed slightly. I've updated the dependencies from the README https://github.com/ddclient/ddclient/tree/v3.9.1 .

I had a couple of questions:
1) How are optional dependencies generally handled? JSON, IPv6 and SSL seem to be optional. Currently I've added them all to the runtime dependencies.
2) Should the REVISION remain at 1 or be reset to 0 when upgrading versions? I've left it as 1.

I lack the knowledge of Perl to do the security review that the Porting guide mentions, so please could someone take a look (if it's necessary).

Finally, I don't have commit access to CVS. If this looks alright, please could someone run the committing commands?

Thanks!

Reeto