Upgrading the Tcl examples wrt. VTK 6.x

Most of them needed invoking the method 'Start' over the object
'iren'. Other examples needed upgrading the code following the
directions given at http://www.vtk.org/Wiki/VTK/VTK_6_Migration_Guide

Change-Id: If092043a7a9ecda1ccea941281775bff28623d56
Merge topic 'FIX_TCL_EXAMPLES_WRT_VTK6.XX' into master

6653cd05 Upgrading the Tcl examples wrt. VTK 6.x