Use vtk_test_cxx_executable in Rendering/GL2PS/Testing/Cxx

Replace the last use of vtkTestingObjectFactory.cmake and remove it.
CMake modules that have immediate inline effects are hard to follow, so
drop this one.

Change-Id: I813644b0c31c1eecd3415f11e57e703d035940fd
Remove references to old VTKData/Baseline directories

The VTKData repository no longer holds Baseline directories so drop
references to such directories from the VTK source tree:

* Replace the default -V in CMake/vtkTestingRenderingDriver.cmake with a
  value that will fail but indicate what to do.  All current uses of
  this module have an explicit -V so the default should never be used.

* Drop a few leftover Baseline directory references from comments in
  "*/*/Testing/*/CMakeLists.txt".

* Remove boilerplate duplicate test command-line examples (that
  reference Baseline directories) from *.py tests and leave an updated
  example in "Wrapping/Python/README.txt".  The command-line example
  convention was added long before the modern CTest infrastructure
  and is no longer needed anyway.

Change-Id: I3001e99b3cc8c2717107e61b3b7f988caeb49cab
Merge topic 'cleanup-vtkTestingObjectFactory-cmake' into master

57569cc9 Use vtk_test_cxx_executable in Rendering/GL2PS/Testing/Cxx
Search for Ghostscript only when needed

Move the search for the Ghostscript executable added by commit 870dd114
(Add new GL2PS testing system using ghostscript, 2012-10-01) into a
dedicated vtkGhostscript module.  Include it from CMakeLists.txt that
need VTK_GHOSTSCRIPT_EXECUTABLE.  This avoids keeping module-specific
code in the top-level CMakeLists.txt file and enables the corresponding
tests in the Testing/External build.

Change-Id: I410737f16c653aaaa60799ce1471cb1798707079
Merge topic 'cleanup-Ghostscript-search' into master

fb82c67a Search for Ghostscript only when needed
BUG #14086: Fix vtkImageAppend when no active scalars are present.

vtkImageAppend failed when the image data didn't have any point-arrays marked as
scalars. Though vtkImageAppend's execution handled that case correctly, the
initialization did not. This patch fixes the initialization code.

Change-Id: I9207646b13038a96a26051fc3aed6d554a55aaf3
Merge topic 'fix-image-append' into master

710ce99d BUG #14086: Fix vtkImageAppend when no active scalars are present.
Merge topic 'cleanup-Baseline-references' into master

fc5d874c Remove references to old VTKData/Baseline directories
Merge branch 'fix-image-append-rel' into release

Change-Id: I8233c8cbb425523d774d32032956e767b64524a5
Merge branch 'release'

Change-Id: Ice402567fc1cd085f7eeecb67d61ede4acdcc342