For a given port determine its dependencies using any combination of the
 - FETCH_DEPENDS
 - EXTRACT_DEPENDS
 - PATCH_DEPENDS
 - LIB_DEPENDS
 - BUILD_DEPENDS
 - RUN_DEPENDS
 - TEST_DEPENDS

and show them as a pseudo graphical tree with indication of the depends type.
Use back references for cross-connections.

WWW: https://sourceforge.net/projects/porttree/
