How to add optional dependencies?

[Jens Rehsack <rehsack%web.de@localhost>]

Hi,

according to PR's pkg/39541, pkg/39542 and pkg/39543 I have one question: 
how can I add optional dependencies (e.g. devel/p5-IO-Socket depends on
net/p5-Net-LibIDN, if available or special wanted or so)?

The background is, PPI, IO::Socket (and some other CPAN modules) configures
themself dependend whether those modules are installed or not. When I create
packages (*.pkg), I want the dependencies recorded, so that I don't need
manually interact which additional pkg's must be installed to get PPI
running as wanted etc.

Best regards,
Jens