Sketcher: Validation tool improvement

======================================

The sketch validation tool offers the functionality to detect missing coincidences. It is a problem that internal geometry causes detected missing coincidences.

Additionally, the tool only shows the visible profile and not the construction geometry.

This commit introduces the ignoring of construction geometry, which "fixes" the two behaviours indicated above.

fixes #3298

src/Mod/Sketcher/Gui/TaskSketcherValidation.cpp

@@ -179,6 +179,10 @@ void SketcherValidation::on_findButton_clicked()
     const std::vector<Part::Geometry *>& geom = sketch->getInternalGeometry();
     for (std::size_t i=0; i<geom.size(); i++) {
         Part::Geometry* g = geom[i];
+
+        if(g->Construction)
+            continue;
+
         if (g->getTypeId() == Part::GeomLineSegment::getClassTypeId()) {
             const Part::GeomLineSegment *segm = static_cast<const Part::GeomLineSegment*>(g);
             VertexIds id;