Fix crash on tortuosity module

The crash happened on data with multiple vessels. The index used in
the filter->GetInflectionPointValue simply wasn't correct.

Also remove the debug array "NumberOfPoints" that had managed to slip
through.
Merge pull request #366 from vovythevov/TortuosityModule-FixMultipleVesselsCrash

Fix crash on tortuosity module
Fix spatial object tubes display

This was forgotten during the update to VTK6. The method
SetInputToPolyDataPipeline actually had to be rewritten.
Merge branch 'UpgradeToVTK6-FixTubeDisplay'

* UpgradeToVTK6-FixTubeDisplay:
  Fix spatial object tubes display
Fix tortuosity CSV export

During the last refactor, the array overzealously removed. It is needed by
the export csv code.
The array was re-installed and documentation updated to prevent this
problem from happening again. Also made the code more robust and more
explicit by checking for possibles failures more often.
Merge branch 'FixTortuosityExportCSV'

* FixTortuosityExportCSV:
  Fix tortuosity CSV export