COMP: Increasing test tolerance for machine variations
COMP: Relaxing tolerance requirements
Merge pull request #319 from aylward/TextTolerance

Text tolerance
COMP: Fix warnings on signed/unsigned comparison
Merge pull request #320 from aylward/DashboardWarningsSignedComp

COMP: Fix warnings on signed/unsigned comparison
BUG: RidgeExtractor set xstep to 3-vector regardless of image dim
BUG: Use NRRD for the 6D ImageIO instead of MetaImage.

Try to avoid some 'double free or memory corruption' errors.
Merge pull request #321 from aylward/RidgeExtractorDimensionalityBug

BUG: RidgeExtractor set xstep to 3-vector regardless of image dim
Fix Convert TRE xml and readme
Improve spatial object node support

The vtkMRMLSpatialObjectNode used to only support VesselTubeSpatialObjects
which can be a problem as the files from Convert TRE can be only
TubeSpatialObjects (VesselTubeSpatialObject's superclass).
This commit allow the vtkMRMLSpatialObjectNode to support loading
TubeSpatialObject.
Also replace static_cast by dynamic_cast.
Merge pull request #322 from thewtex/nrrd6d

BUG: Use NRRD for the 6D ImageIO instead of MetaImage.
Merge pull request #324 from vovythevov/MiscTubeTKFixes

Misc tube tk fixes