rdeps graph

[Ryan Schmidt]

The port-rdeps script had an option I used often to generate a Graphviz graph of the dependencies, but port-rdeps was slow; MacPorts 1.9's "port rdeps" is much faster so I'd rather use that. But it doesn't seem to have Graphviz graph generation, right? If I'm seeing that right, then I might dive in to try to add that (in src/port/port.tcl in action_deps, looks like?), maybe get a little more familiar with base code.