Port :
======

   Ports represent communication end-points.  They are round-shaped,
and reside on boxes boundaries.

   How to create a port:
1- select the <ObjectsEdit>:<Ports>:<Create> menu button
   (or type 'p' in the window where you want to create a port
    it will select the same menu mode)
2- click with the mouse left button inside the desired box. The
   port will be placed at the nearest projected location on the
   box boundary.

   Ports can be connected together either:
- graphically, by drawing edges connecting a port to another port
  or a multi-synchronisation "web"
- textually, by label identifications.

Ports are selected/moved/killed along with their support box. They
can also be moved or killed independantly.

WARNING: not yet implemented:
   Ports may be evenly distribute on a box segment.

   When system flags "align" is on, ports locations are straightened
at move to align as much as possible respective to outgoing edges.


 Port size attributes can be fixed by resources:
        atg*portRadius : 5
        atg*portLineWidth: 0 (mean 1 but draw by fast raster)