cp: fix the --no-preserve=mode option

cp: fix the --no-preserve=mode option

The --no-preserve=mode option did not do what its name implies:
it would mistakenly preserve permission mode bits.
* NEWS: Mention the fix.
* TODO: Remove an entry.
* src/copy.c (copy_reg): Add a condition to properly
handle the --no-preserve=mode option for files
(copy_internal): Add a condition to properly handle the
--no-preserve=mode option for directories.
* src/copy.h (struct cp_options): Add a new boolean.
* src/cp.c (cp_option_init,decode_preserve_arg): Set the
new boolean value according to specified options.
* src/install.c (struct cp_options): Initialize the new boolean.
* src/mv.c (struct cp_options): Initialize the new boolean.
* tests/cp/preserve-mode.sh: Add a new test.
* tests/cp/link-preserve.sh (-a --no-preserve=mode): Adjust the
expected perms: now, --no-preserve=mode overrides the --preserve=mode
that is inherent in -a, as it should.
* tests/local.mk: Add the new test to the list.