basename,dirname,freeramdisk,rx,raidautorun,runsv,chvt: skip "--" argument

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/libbb/single_argv.c b/libbb/single_argv.c
index 85137b4..64844dd 100644
--- a/libbb/single_argv.c
+++ b/libbb/single_argv.c
@@ -10,6 +10,8 @@
 
 char* FAST_FUNC single_argv(char **argv)
 {
+	if (argv[1] && strcmp(argv[1], "--") == 0)
+		argv++;
 	if (!argv[1] || argv[2])
 		bb_show_usage();
 	return argv[1];