BUG: make sure the module is selected before running self test

When running on the factory as a ctest, slicer will start with
the default module selected.  Since the module has not been
entered yet, the slicer.modules.LandmarkRegistrationWidget will
not exist yet.  So select the module as the start of
each test case.
Change name of method and make it more robust
COMP: Add VTK 6 support
Merge pull request #8 from finetjul/vtk-6-support

COMP: Add VTK 6 support
Handle case of missing volume node for fiducial list

This can happen during automatic node add/delete opertations that
trigger events on a scene in transition.  We'll just be defensive here
so that we don't generate errors.  This fixes the py_LandmarkRegistration
test errors on the dashboard.
Make use of new end moving event for fiducials

Allows plugins to perform specific tasks when the mouse button is
released.
Remove some debug statements
Improve the git ignore options
Fix the Affine plugin

Make the rigid/similarity/affine buttons work

Generalize the transforms overall
Update to support abstract transforms for nonlinear

Interactive thin plate!
Remove debug statements and hanlde VTKv6 changes.
Fix bug exposed by testing with VTKv6

Due to the way the code is structured, the extent variable
contained a mix of ints and floats.  This was an acceptable
argument for the VTKv5, method but VTKv6 is more strictly correct
on this point.
Always set the transform for affine plugin

This allows the user go go back and forth between registration
plugins using the same landmarks.
Remove unneeded version conditional for vtkTransformToGrid

It turns out that since this class is not pipelined, the method
SetInput was not changed.
Some visualization improvmeents

Add flicker mode.
Speed up rocking.
Fix method naming mismatch between vtk 5 and 6

While the vtkTransformToGrid method name didn't change,
the vtkGridTransform method name did change ;)
Map new fiducials through current transform

This simplifies the process of adding new landmarks to a registration
in progress, since the new points will be in the right approximate
location as determined by the current transform.  That is, the new
information added by the pair of points should not cause a change
to the calculation of something like a thin plate spline except perhaps
adding extra weight in a region.
Avoid spurious messages during event processing
Reset fade slider when done flickering
ENH: don't make newly added points stay within volume.

This makes it easier to move them to the correct spot when the
two volumes are not overlapping initially.