COMP: Update CTK project - Fix compilation error when python is disabled

$ git shortlog 68a1ce2..1c97e54 --no-merges
Dzenan Zukic (1):
Ensure CTKVisualizationVTKWidget build with VTK6 and python disabled.

Sascha Zelzer (2):
Added an option to skip install commands for plugins.
Using : as separator might conflict with absolute paths on Windows.

From: Dzenan Zukic <dzenan.zukic@kitware.com>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23770 3bd1e089-480b-0410-8dfb-8563597acbee