Giuseppe D'Angelo authored Jan 29, 2013 and David Gobbi committed Jul 10, 2013

vtkContourFilter uses several specialized subfilters depending
on the input data type to perform the contouring. However, the
progress from these subfilters wasn't pushed through the
vtkContourFilter object. This patch installs an observer on
the subfilter and properly updates vtkContourFilter's progress.

The work for this patch has been sponsored by BP.

Change-Id: I849b442318b0a59a64099add2fa6ccd74967725a