request now uses exported PREFIX

See merge request fsl/fslpy!44

Modified to request install

See merge request fsl/fslpy!43

  - if moving a file from a group, need to remove the entire group
  - Special test for when dest is a non-existent directory

dirname. Make it abs

called() to get the function.

Auto install links to scripts

See merge request fsl/fslpy!42

broken.