utils.py: Dont stomp on non-empty directories with symlinks
Instead of recursively removing a directory for the sake of replacing it with a symlink, issue a warning.
This should arguably be turned into an error, but it's unclear to me
- What the ultimately desirable behavior should be
- Whether this breaks projects which currently make the assumption that this is OK
This is an improvement over the old behavior, believe we should live with the warnings and possibly strengthen this into an error at a later time.