Fix the tcl and python cells test

Both tests were relying on IO/Export to be included. With OpenGL2 we
do not build IO/Export by default and we do nto want to make testing
depend on it. So these tests have been modified to work without
requiring IO/Export.

At the same time this test identified an issue with Positional lights
that I was able to fix which resulted in cleaner shader code. The key
was that distance can be computed in view coordinates just as easily
as in world coordinates.  This is because View coordinates is just a
rotation and translation of world coordinates so distances are not
impacted.

Change-Id: Icf74211daa164f6a3c49301f26e32571546e38d1
Merge topic 'fix_cells_tests' into master

4dc092c0 Fix the tcl and python cells test