ls --color: Don't stat symlinks when neither ORPHAN nor MISSING attribute has a color.

ls --color: Don't stat symlinks when neither ORPHAN nor MISSING attribute has a color.
* src/ls.c (main): Don't set check_symlink_color when C_EXEC is
colored, unless ln=target (aka color_symlink_as_referent) is set.
(gobble_file): Set f->linkok = true also when !check_symlink_color.
http://thread.gmane.org/gmane.comp.gnu.coreutils.bugs/10608/focus=10927
Reported by Jeremy Maitin-Shepard.
* tests/strace: New file, contents extracted from...
* tests/mv/atomic: ...here.  Source strace.
* tests/ls/stat-free-symlinks: New file.  Test for the above.
Use strace to ensure that in this corner case, ls does not call stat.
* tests/ls/Makefile.am (TESTS): Add stat-free-symlinks.
* tests/Makefile.am (EXTRA_DIST): Add strace.