Made code compatible with VTK 6 while maintaining VTK 5 compatibility

- replaced obsolete vtkFloatingPointType with double
- conditionally use new pipeline method SetInputData
- use SetInputConnection instead of SetInput even on VTK 5
- removed unnecessary Update() in vtk2gts since all call to it have already called Update on the object
- also suppress some GCC and clang warnings with #pragma
- removed obsolete vtkCxxRevisionMacro
- made private methods static, to fix warnings
- added assertion