ls: with -LR, exit with status 2 upon detecting a cycle

ls: with -LR, exit with status 2 upon detecting a cycle

* src/ls.c (print_dir): Diagnosing the cycle is not enough.
Also set exit status to 2.  This is what Solaris' /bin/ls does, too.
* tests/ls/infloop: Rework test: match both expected stdout and stderr.
Require an exit status of 2 in this case.
* doc/coreutils.texi (ls invocation): Mention that a loop provokes
in an exit status of 2.
* NEWS (Bug fixes): Mention it.
Reported by Yang Ren in http://bugzilla.redhat.com/525402.
* THANKS: Correct ordering of Yang Ren's names.