Implement multi-sample antialiasing on OS X.

Set the necessary attributes to create a sample buffer for the
OpenGL context of the vtkCocoaRenderWindow.  This allows VTK to
do anti-aliased rendering in the window.  However, multisampling
is turned off by default on OS X because it causes rendering
problems on some Mac models.

Change-Id: I0ff8073e38d8a63e637cfe4e7146e2d1327d65eb
Performance improvement to CellToPoint.

Using faster API to import performance of vtkCellDataToPointData.
vtkCellDataToPointData was using ds->GetCell(..)->GetPointIds() which is
considerably slower than directly calling ds->GetCellPoints(...). That change
considerably improves the speed of this filter.

Change-Id: I99660cde38a1b359b76d8c71b673d5ae9a229507
Merge topic 'speedup_point2cell' into master

038024b7 Performance improvement to CellToPoint.
Add a breadcrumb to guide new developers to the developers guide.

Change-Id: I45df8e4d2f7931ed3cb0b044f9b15af67e2ca8dc
Merge topic 'add-documentation-describing-how-to-contribute' into master

cf632584 Add a breadcrumb to guide new developers to the developers guide.
Merge topic 'osx-multi-samples' into master

23f6ba79 Implement multi-sample antialiasing on OS X.