X3D: Don't write line-no into objects by default

This is handy for debugging, not general use.
so only do this when DEBUG is set.

Also use a custom property instead of registering RNA.

io_scene_x3d/import_x3d.py

@@ -3024,10 +3024,12 @@ def importShape_ProcessObject(vrmlname, bpydata, geom, geom_spec, node,
     # the data
     # bpymesh.transform(getFinalMatrix(node))
     bpyob = node.blendObject = bpy.data.objects.new(vrmlname, bpydata)
-    bpyob.source_line_no = geom.lineno
     bpyob.matrix_world = getFinalMatrix(node, None, ancestry, global_matrix)
     bpy.context.scene.objects.link(bpyob).select = True
 
+    if DEBUG:
+        bpyob["source_line_no"] = geom.lineno
+
 
 def importText(geom, ancestry, bpyima):
     fmt = geom.getChildBySpec('FontStyle')
@@ -3454,12 +3456,6 @@ def load_web3d(path,
     # Used when adding blender primitives
     GLOBALS['CIRCLE_DETAIL'] = PREF_CIRCLE_DIV
 
-    # Enable custom property for source line number
-    if not hasattr(bpy.types.Object, "source_line_no"):
-        bpy.types.Object.source_line_no = bpy.props.IntProperty(
-            name="Source Line #",
-            description="Node position in the source X3D/VRML file")
-
     #root_node = vrml_parse('/_Cylinder.wrl')
     if path.lower().endswith('.x3d'):
         root_node, msg = x3d_parse(path)