show waterway ways with priority (especially smaller ones like waterway=stream)

[mnalis]

Sometimes smaller waterways are tagged just as a linear way e.g. waterway=stream, and they may be drawn over areas marked with e.g. landuse=*

When that happens, result is that only landuse is rendered, and waterway is invisible. It would be better if waterway was rendered on top of that landuse area (unless it was tunnel=culvert)

e.g. here the waterway=stream is practically invisible, but should be visible.

[waldyrious]

Cross-linking the related #33 for reference.