rm could be tricked into mistakenly reporting a cycle.

rm could be tricked into mistakenly reporting a cycle.
* src/remove.c: [cycle_check_state]: New global.
(remove_cwd_entries): Adapt to new semantics of cycle_check.
(rm): Call cycle_check_init and cycle_check_free for each file.

When rm detects a cycle, don't abort the entire command,
but rather just the affected command line argument.
* src/remove.c: Include <setjmp.h>
(struct dirstack_state) [current_arg_jumpbuf]: New member.
(remove_cwd_entries): Call longjmp if we detect a cycle.
(rm): Call setjmp here.

* src/remove.c (cycle_check, is_power_of_two): Remove functions.
Instead, include cycle-check.h and use it.