mv and "cp -r" no longer fail when invoked with two arguments

mv and "cp -r" no longer fail when invoked with two arguments
where the first one names a directory and the second name ends in
a slash and doesn't exist.  E.g., "mv dir B/", for nonexistent B,
now succeeds, once more. This reverts part of the 2004-06-27
change for 5.3.0.
* NEWS: Say the above.
* src/mv.c (target_directory_operand): Don't require (here)
that the target operand "look like" a directory.  This change
pushes the test down to the rename syscall level, where a
"mv dir existing-non-dir/" will mistakenly succeed on older systems
that ignore trailing slashes in the rename destination argument.
* src/cp.c (target_directory_operand): Likewise, but for cp.
* tests/mv/trailing-slash: Exercise the above fixes.
* tests/cp/trailing-slash: New file.
* tests/cp/Makefile.am (EXTRA_DIST): Add trailing-slash.