Through cleanup.  Much of `bacom-postprocess' was removed.
If necessary some of it can be done by the user in a yet to be
provided hook.  In particular we do not either remove nor add any
trailing whitespace.  Try to delegate this job the the completion UI;
we just provide the completion candidates.
`bacom-addsuffix' now uses `comint-directory' in the hope that it could help to make this library work for remote shells.