"ls --color" would highlight other-writable and sticky directories

"ls --color" would highlight other-writable and sticky directories
no differently than regular directories on a file system with
dirent.d_type support.
* NEWS: Say the above.
* src/ls.c (gobble_file): With --color, also stat the file when
we know it is a directory.
Derived from an anonymous one-line fix and bug report:
<https://savannah.gnu.org/bugs/?15043>.
* tests/ls/color-dtype-dir: New file.  Test for the above fix.
* tests/ls/Makefile.am (TESTS): Add color-dtype-dir.