Cropping: be more verbose when output dir isn't accessible
Cropping: be more verbose when output dir isn't accessible

If the requesting user is a super user and the output path can't be accessed,
the error message now contains the assumed path.

htem/CATMAID,htem/CATMAID,fzadow/CATMAID,fzadow/CATMAID,htem/CATMAID,fzadow/CATMAID,htem/CATMAID,fzadow/CATMAID