ViewProvider(DocumentObject): new APIs for context aware selection

Context aware selection makes it possible to select the same Coin3D node
in different hierarchies (i.e. context) without ambiguity.

New/modified APIs in ViewProvider (the first two are the most crucial
APIs for context aware selection to work):

* getElementPicked(), supercedes getElement(). Given a Coin3D pick
  point, this function returns a dot separated subname reference as a
  path leads to the selected object.

* getDetailPath(), supercedes getDetail(). Given a subname reference,
  this function returns an SoFullPath leads to the Coin3D node of the
  selected object or sub-element (with SoDetail).

* (has)HiddenMarker(), check/return a special text marker for context
  aware override of object visibility.

* partialRender(), render only part of the object based on given
  subname references. It can render, e.g. some faces of a solid, or
  some children of a container. It uses the 'secondary' extension of
  SoSelectionElementAction to select which elements to render or hide.
  The actually rendering functionality will be added in the following
  patch.

* update()/onChanged(), modified to sync Visibility property from
  DocumentObject.

* useNewSelectionModel(), modified to return the default true view
  parameter. This is for test in the early stage of Link development,
  probably not needed anymore.

* getBoundingBox(), a convenience function to obtain the bounding box
  of a sub-object/element regardless of object's visibility. It uses
  getDetailPath() and SoGetBoundingBoxAction to obtain bounding box
  through Coin3D. It will be used in later sub-element box selection
  functionality.

New/modified APIs in ViewProviderDocumentObject:

* getElementPicked()/getDetailPath() provides actual implementation to
  support container like (sub)object selection without ambiguity. It
  relies on DocumentObject::getSubObject() to walk the path.

* reattach(), called when undo deleteion

* forceUpdate()/isUpdateForced(), force update even if object is
  invisible. These are used by Link to force update the visual of a
  linked object regardless of its visibility.

* getLinkedViewProvider(), return the linked view provider with
  hierarchy.

ViewProviderDocumentObjectPy:

* Object attribute is made writtable. Assigning it is equaivalant of
  calling ViewProviderDocumentObject::attach() in Python.

src/Gui/ViewProviderDocumentObjectPyImp.cpp

@@ -29,7 +29,7 @@
 
 #include <Gui/ViewProviderDocumentObject.h>
 #include <Gui/Document.h>
-#include <App/DocumentObject.h>
+#include <App/DocumentObjectPy.h>
 
 // inclusion of the generated files (generated out of ViewProviderDocumentObjectPy.xml)
 #include "ViewProviderDocumentObjectPy.h"
@@ -62,6 +62,27 @@ Py::Object ViewProviderDocumentObjectPy::getObject(void) const
     return Py::Object(obj->getPyObject(), true); // do not inc'ref twice
 }
 
+void ViewProviderDocumentObjectPy::setObject(Py::Object pyobj)
+{
+    if(!PyObject_TypeCheck(*pyobj,&App::DocumentObjectPy::Type))
+        throw Py::TypeError("Expect document object");
+    App::DocumentObject* obj = getViewProviderDocumentObjectPtr()->getObject();
+    if(obj)
+        throw Py::RuntimeError("View object already attached");
+    getViewProviderDocumentObjectPtr()->attach(
+            static_cast<App::DocumentObjectPy*>(*pyobj)->getDocumentObjectPtr());
+}
+
+Py::Boolean ViewProviderDocumentObjectPy::getForceUpdate() const 
+{
+    return Py::Boolean(getViewProviderDocumentObjectPtr()->isUpdateForced());
+}
+
+void ViewProviderDocumentObjectPy::setForceUpdate(Py::Boolean arg)
+{
+    getViewProviderDocumentObjectPtr()->forceUpdate(arg);
+}
+
 Py::Object ViewProviderDocumentObjectPy::getDocument(void) const
 {
     Document* doc = getViewProviderDocumentObjectPtr()->getDocument();