Waterway routing on stream

[A. Fischer]

Coming from a discussion about river / stream (in German OSM forum https://forum.openstreetmap.org/viewtopic.php?id=72805)

I'd like to think about some changes, but not again the river/stream tagging rules:

Waterway routing is mainly done on waterway=river|canal. But there are some ways with stream tag and boat=yes.

waterway=stream has 14M entries but only around 1060 with a boat=yes.
So it is not a good idea to add waterway=stream to the lookup.dat.

What to do when still want to impove waterway routing?
I see three ways:

- Add a boat=yes to all.brf
  this collect also the streams with this tag but you get no qualifier for the kind of waterway.

- Extract all waterway=stream with boat=yes from world file, remove it from world file and add the collection. Clean, but very heavy stuff.

- Add a rule in BRouter source, possible, but this is hard coded
  e.g in OsmCutter/nextWay something like
      if (w.getTag( "waterway" ) != null
        && w.getTag("waterway").equals("stream")
        && w.getTag( "boat" ) != null
        && w.getTag("boat").equals("yes")) {
        // add
    } else {
        // no entry
    }

What do you think?

This also needs a review for
  waterway=ditch 2.8M around 200 boat=yes

  waterway=drain 1.2M around 200 boat=yes