Fix comments for switch statement fall throughs

This cleans up all GCC warnings (-Wimplicit-fallthrough=2) about
implicitly falling through switch cases.

3d-viewer/3d_rendering/3d_render_raytracing/accelerators/cbvh_pbrt.cpp

@@ -555,12 +555,12 @@ BVHBuildNode *CBVH_PBRT::recursiveBuild ( std::vector<BVHPrimitiveInfo> &primiti
                           (mid <= end) );
 
                 if( (mid != start) && (mid != end) )
-                    // for lots of prims with large overlapping bounding boxes, this
-                    // may fail to partition; in that case don't break and fall through
-                    // to SPLITMETHOD::EQUAL_COUNTS
                     break;
             }
 
+            // Intentionally fall through to SPLITMETHOD::EQUAL_COUNTS since prims
+            // with large overlapping bounding boxes may fail to partition
+
             case SPLITMETHOD::EQUALCOUNTS:
             {
                 // Partition primitives into equally-sized subsets

common/common.cpp

@@ -415,7 +415,7 @@ wxString KIwxExpandEnvVars(const wxString& str)
 
                 break;
             }
-            //else: fall through
+            // else fall through
 
         default:
             strResult += str_n;

common/plotters/GERBER_plotter.cpp

@@ -824,7 +824,7 @@ void GERBER_PLOTTER::FlashPadRect( const wxPoint& pos, const wxSize& aSize,
     case 900:
     case 2700:        // rotation of 90 degrees or 270 swaps sizes
         std::swap( size.x, size.y );
-        // Pass through
+        // Intentionally fall through
     case 0:
     case 1800:
         if( trace_mode == SKETCH )

common/widgets/lib_tree.cpp

@@ -358,7 +358,7 @@ void LIB_TREE::onQueryCharHook( wxKeyEvent& aKeyStroke )
             toggleExpand( sel );
             break;
         }
-        /* fall through, so the selected component will be treated as the selected one */
+        // Intentionally fall through, so the selected component will be treated as the selected one
 
     default:
         aKeyStroke.Skip(); // Any other key: pass on to search box directly.

cvpcb/cvpcb_mainframe.cpp

@@ -566,6 +566,8 @@ void CVPCB_MAINFRAME::SetFootprintFilter(
         // Extract the current search patten when needed
         m_currentSearchPattern = m_tcFilterString->GetValue();
 
+        // Intentionally fall through since this uses the filter options passed in
+
     case FOOTPRINTS_LISTBOX::UNFILTERED_FP_LIST:
     case FOOTPRINTS_LISTBOX::FILTERING_BY_PIN_COUNT:
     case FOOTPRINTS_LISTBOX::FILTERING_BY_LIBRARY:

eeschema/netlist_object_list.cpp

@@ -114,6 +114,8 @@ bool NETLIST_OBJECT_LIST::BuildNetListInfo( SCH_SHEET_LIST& aSheets )
             if( net_item->GetNet() != 0 )
                 break;
 
+            // Intentionally fall through if there is no net assigned
+
         case NET_SEGMENT:
             // Test connections point to point type without bus.
             if( net_item->GetNet() == 0 )
@@ -162,6 +164,8 @@ bool NETLIST_OBJECT_LIST::BuildNetListInfo( SCH_SHEET_LIST& aSheets )
             if( net_item->m_BusNetCode != 0 )
                 break;
 
+            // Intentionally fall through if there is no bus assigned
+
         case NET_BUS:
             // Control type connections point to point mode bus
             if( net_item->m_BusNetCode == 0 )

pcbnew/class_module.cpp

@@ -843,7 +843,7 @@ SEARCH_RESULT MODULE::Visit( INSPECTOR inspector, void* testData, const KICAD_T
             if( result == SEARCH_RESULT::QUIT )
                 break;
 
-        // m_Drawings can hold TYPETEXTMODULE also, so fall thru
+        // Intentionally fall through since m_Drawings can hold TYPETEXTMODULE also
 
         case PCB_MODULE_EDGE_T:
             result = IterateForward<BOARD_ITEM*>( m_drawings, inspector, testData, p );

pcbnew/dialogs/dialog_pad_properties.cpp

@@ -1282,7 +1282,7 @@ bool DIALOG_PAD_PROPERTIES::padValuesOK()
         if( padlayers_mask[B_Paste] || padlayers_mask[F_Paste] )
             error_msgs.Add( _( "Error: Connector pads are not on the solder paste layer\n"
                                "Use SMD pads instead" ) );
-        // Fall trough
+        // Intentionally fall through
     case PAD_ATTRIB_SMD:       // SMD and Connector pads (One external copper layer only)
         {
         LSET innerlayers_mask = padlayers_mask & LSET::InternalCuMask();

pcbnew/exporters/export_vrml.cpp

@@ -1160,6 +1160,8 @@ static void export_vrml_padshape( MODEL_VRML& aModel, VRML_LAYER* aTinLayer, D_P
         pad_dx  = 0;
         pad_dy  = 0;
 
+        // Intentionally fall through and treat a rectangle as a trapezoid with no sloped sides
+
     case PAD_SHAPE_TRAPEZOID:
         {
         double coord[8] =

pcbnew/gpcb_plugin.cpp

@@ -753,7 +753,7 @@ void GPCB_FPL_CACHE::parseParameters( wxArrayString& aParameterList, LINE_READER
             // Element descriptions can span multiple lines.
             line = aLineReader->ReadLine();
 
-            // Fall through is intentional.
+            // Intentionally fall through
 
         case '\t':
         case ' ':