Copy URL to NEWNAME. Both args must be strings.
Signals a `file-already-exists' error if file NEWNAME already exists,
unless a third argument OK-IF-ALREADY-EXISTS is supplied and non-nil.
A number as third arg means request confirmation if NEWNAME already exists.
This is what happens in interactive use with M-x.
Fourth arg KEEP-TIME non-nil means give the new file the same
last-modified time as the old one. (This works on only some systems.)
Fifth arg PRESERVE-UID-GID is ignored.
A prefix arg makes KEEP-TIME non-nil.
(fn URL NEWNAME &optional OK-IF-ALREADY-EXISTS KEEP-TIME PRESERVE-UID-GID)