C++/mex files: large cleanup

5_reconstruction/gtDilateGrains.m

zUtil_Cxx/6D_ops/gt6DBlobsToSingleSino_c.cpp

zUtil_Cxx/6D_ops/gt6DSingleSinoToBlobs_c.cpp

zUtil_Cxx/6D_ops/gt6DUpdateDualDetector_c.cpp

zUtil_Cxx/6D_ops/gt6DUpdateDualL1_c.cpp

zUtil_Cxx/6D_ops/gt6DUpdatePrimal_c.cpp

zUtil_Cxx/CompressiveSensing/gtSoftThreshold.cpp

...ell_operations/internal_cell_blobs_to_single_sinogram.cpp

..._Cxx/cell_operations/internal_cell_blobs_to_sinograms.cpp

...ell_operations/internal_cell_single_sinogram_to_blobs.cpp

..._Cxx/cell_operations/internal_cell_sinograms_to_blobs.cpp

...cell_operations/internal_cell_sum_FISTA_scaled_assign.cpp

...x/cell_operations/internal_cell_sum_FISTA_scaled_copy.cpp

...rations/internal_cell_sum_FISTA_scaled_non_neg_assign.cpp

zUtil_Cxx/gtCxxDilateGrainsVoxel.cpp

zUtil_Cxx/gtImgMeanValue.cpp

zUtil_Cxx/gtMathsRotationTensor_c.cpp

zUtil_Cxx/include/gtCxxMathsSumCellVolumes.h

zUtil_Cxx/internal_gtAssignGrainToVol.cpp

zUtil_Cxx/internal_gtAssignGrainToVol_interf.cpp