When knocking out higher-priority zone use fill, not outline.

Also fixes a bunch of naming issues, primarily with lowercase for
protected variables, but also some for consistency with other parts
of the code.

Also changes the zone fill radio buttons in Board Setup to be more
generic referring to legacy vs. current, and to have tooltips.

Fixes https://gitlab.com/kicad/code/kicad/issues/5583

pcbnew/plot_board_layers.cpp

@@ -492,6 +492,8 @@ void PlotStandardLayer( BOARD *aBoard, PLOTTER* aPlotter,
 
     for( ZONE_CONTAINER* zone : aBoard->Zones() )
     {
+        int outlineThickness = zone->GetFilledPolysUseThickness() ? zone->GetMinThickness() : 0;
+
         for( PCB_LAYER_ID layer : zone->GetLayerSet().Seq() )
         {
             auto pair = std::make_pair( layer, zone );
@@ -529,17 +531,12 @@ void PlotStandardLayer( BOARD *aBoard, PLOTTER* aPlotter,
                 if( candidate->GetNetCode() != zone->GetNetCode() )
                     continue;
 
-                // Merging zones of the same net can be done only for areas
-                // having compatible settings for drawings:
-                // use or not outline thickness, and if using outline thickness,
-                // having the same thickness
-                // because after merging only one outline thickness is used
-                if( candidate->GetFilledPolysUseThickness() != zone->GetFilledPolysUseThickness() )
-                    // Should not happens, because usually the same option is used for filling
-                    continue;
+                // Merging zones of the same net can be done only for areas having compatible
+                // settings for filling as the merged zone can only have a single setting.
+                int candidateOutlineThickness = candidate->GetFilledPolysUseThickness() ?
+                                                    candidate->GetMinThickness() : 0;
 
-                if( zone->GetFilledPolysUseThickness()
-                        && ( candidate->GetMinThickness() != zone->GetMinThickness() ) )
+                if( candidateOutlineThickness != outlineThickness )
                     continue;
 
                 plotted.insert( candidate_pair );
@@ -867,9 +864,9 @@ void PlotSolderMaskLayer( BOARD *aBoard, PLOTTER* aPlotter, LSET aLayerMask,
                 continue;
 
             // add shapes inflated by aMinThickness/2 in areas
-            zone->TransformOutlinesShapeWithClearanceToPolygon( areas, inflate + zone_margin );
+            zone->TransformSmoothedOutlineWithClearanceToPolygon( areas, inflate + zone_margin );
             // add shapes with their exact mask layer size in initialPolys
-            zone->TransformOutlinesShapeWithClearanceToPolygon( initialPolys, zone_margin );
+            zone->TransformSmoothedOutlineWithClearanceToPolygon( initialPolys, zone_margin );
         }
 
         int maxError = aBoard->GetDesignSettings().m_MaxError;