1) I replaced all `ERROR: Unsuccessful` undescriptive messages by
   understandable errors; for example, when the symlink would fail,
   no error would show.

2) Also, when a link already existed but wasn't working (i.e., kpsewhich
   could not find it), I propose to remove it and then create the
   symlink.

3) use `mktexlsr --quiet` so that mktexlsr does not clobber stdout
   with useless information.