how to query the dependency graph

[Jeremy Lavergne]

> "man port" is quite informative.  "port rdeps portname" gives you the dependency tree (doesn't really understand general graphs, it assumes simple DAGs) for "portname"; it won't produce e.g. "dot" input for you, though.

We have some dot-oriented scripts available:
https://trac.macports.org/browser/contrib/port-depgraph/port-depgraph
https://trac.macports.org/browser/contrib/port-rdeps/port-rdeps