If NEWNAME is a directory name, copy FILE to a like-named file under
NEWNAME.
+For NEWNAME to be recognized as a directory name, it should name a
+directory and end in a slash.
+
This function always sets the file modes of the output file to match
the input file.
If NEWNAME is a directory name, rename FILE to a like-named file under
NEWNAME.
+For NEWNAME to be recognized as a directory name, it should name a
+directory and end in a slash.
+
Signal a `file-already-exists' error if a file NEWNAME already exists
unless optional third argument OK-IF-ALREADY-EXISTS is non-nil.
An integer third arg means request confirmation if NEWNAME already exists.