matrix.save_transform(): Boost precision
matrix.save_transform(): Boost precision

Increased precision in output transformation matrix text files was necessary to converge the behaviour of population_template on the "dev" branch toward that of 3.0_RC3.

MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3