libbb: make xchroot do a chdir("/") after chroot

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

libbb/xfuncs_printf.c

@@ -362,6 +362,7 @@ void FAST_FUNC xchroot(const char *path)
 {
 	if (chroot(path))
 		bb_perror_msg_and_die("can't change root directory to %s", path);
+	xchdir("/");
 }
 
 // Print a warning message if opendir() fails, but don't die.