Create folder and rename if another has the same name

Create folder and rename if another has the same name and contains at least one file.

USAGE
create_folder(newdir)

Folder "newdir" will be created.

If there is already a folder named "newdir" with any file regardless of the level, it will be renamed to "newdir-backup" (or "newdir-backup02",
"newdir-backup03", ...).

If "newdir" is empty or contains only folders, nothing is done.