update marker tests after d685307250 + add collision boxes to variety of test images

tests/visual_tests/styles/marker-on-hex-grid.xml

@@ -11,6 +11,7 @@
                 placement="line"
                 spacing="50"
             />
+            <DebugSymbolizer />
         </Rule>
     </Style>
     <Layer name="point" srs="+init=epsg:4326">

tests/visual_tests/styles/marker-on-line-spacing-eq-width-overlap.xml

@@ -48,6 +48,7 @@
         <Rule>
             <MarkersSymbolizer file="shape://ellipse" allow-overlap="true" width="20" height="20" placement="line" spacing="15"/>
             <LineSymbolizer stroke-width="0.2" stroke="#ff0000" />
+            <DebugSymbolizer />
         </Rule>
     </Style>
 </Map>

tests/visual_tests/styles/marker-on-line.xml

@@ -7,6 +7,7 @@
 <Style name="point-placement" filter-mode="first" >
   <Rule>
     <MarkersSymbolizer placement="point" marker-type="ellipse" fill="blue" />
+    <DebugSymbolizer />
   </Rule>
 </Style>
 <Layer name="carto_tests">

tests/visual_tests/styles/marker-path-expression.xml

@@ -22,6 +22,7 @@ x,y,FILENAME,FILETYPE
     <Style name="frame">
         <Rule>
             <PointSymbolizer />
+            <DebugSymbolizer />
         </Rule>
     </Style>
 

tests/visual_tests/styles/marker-svg-empty-g-element.xml

@@ -22,6 +22,7 @@ x,y
     <Style name="frame">
         <Rule>
             <PointSymbolizer />
+            <DebugSymbolizer />
         </Rule>
     </Style>
 

tests/visual_tests/styles/marker-vs-point.xml

@@ -53,6 +53,7 @@ x,y
   <Style name="frame">
     <Rule>
       <PointSymbolizer />
+      <DebugSymbolizer />
     </Rule>
   </Style>