Bash completion: Polishing up
Bash completion: Polishing up

* Gracefully handle empty option "-" for use when piping
* When autocompleting input files, also list directories that match

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