* src/copy.c (copy_internal): With -i, prompt even if the source
is a directory and the destination is not. This is required by
POSIX and gives the user a chance to bail out before failing.
* tests/cp/Makefile.am (TESTS): Add cp-i.
* tests/cp/cp-i: New file.
* tests/mv/Makefile.am (TESTS): Add i-5.
* tests/mv/i-5: New file.