test-open: on GNU/Hurd, /dev/null is a directory * tests/test-fopen.h (main): Rename... (test_fopen): ...to this. Use a guaranteed non-directory when confirming open behavior on trailing slash. * tests/test-openat-safer.c (main): Likewise. * tests/test-open.h (main): Likewise.... (test_open): ...to this. * tests/test-fopen.c (main): Adjust caller. * tests/test-fopen-safer.c (main): Likewise. * tests/test-open.c (main): Likewise. * tests/test-fcntl-safer.c (main): Likewise. Reported by Samuel Thibault. Signed-off-by: Eric Blake <ebb9@byu.net>