ls --color: don't emit a final no-op escape sequence

ls --color: don't emit a final no-op escape sequence

* src/ls.c (main): With --color, avoid emitting the final color-
resetting escape sequence when it would be a no-op.
* tests/ls/color-clear-to-eol: Adjust expected output accordingly.
* tests/ls/color-dtype-dir: Likewise.
* tests/ls/multihardlink: Likewise.
* tests/ls/stat-free-symlinks: Likewise.
* tests/misc/ls-misc: Likewise.
* NEWS (Changes in behavior): Mention it.
C de-Avillez rebased and adapted four of the new sl-dangle*
tests in tests/misc/ls-misc.
Reported by Jim Avera in
http://bugs.launchpad.net/ubuntu/+source/coreutils/+bug/494663