expand,unexpand: drop broken test, add FIXME comment

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/coreutils/expand.c b/coreutils/expand.c
index f7e4619..8d064db 100644
--- a/coreutils/expand.c
+++ b/coreutils/expand.c
@@ -63,6 +63,8 @@
 	OPT_ALL         = 1 << 2,
 };
 
+//FIXME: does not work properly with input containing NULs
+
 #if ENABLE_EXPAND
 static void expand(FILE *file, unsigned tab_size, unsigned opt)
 {