symlinks and RENAME-FILE and DELETE-DIRECTORY
Both followed symlinks too eagerly.
* Presumably anyone doing (rename-file "link-to-foo" "bar") wants to rename
the link and not the file it points to -- which has the unpleasant
side-effect of breaking the selfsame link.
Make it so.
* It is less clear what someone doing (delete-directory "link-to-dir")
expects to happen -- so take the conservative option and signal an error,
and document this.