cpdup - Do not create a .tmp file and rename if the target does not exist.

cpdup - Do not create a .tmp file and rename if the target does not exist.

* When copying if the target does not exist use the target's actual name
  instead of the name of a temporary file.

  This helps filesystems (aka HAMMER) which use hashed directories.  Inode
  numbers can be selected by the FS on the basis of the file-name in
  order to maintain directory-order linearity.  If the copy program creates
  the target file with one name and then renames it to the real name,
  however, the feature is lost and we get one big scramble again.