Just to remind:
rename() causes the link named from to be renamed as to. If to exists,
it is first removed. Both from and to must be of the same type (that is,
both directories or both non-directories), and must reside on the same
file system.
rename() guarantees that if to already exists, an instance of to will al-
ways exist, even if the system should crash in the middle of the opera-
tion.
