Refactor, add new helper fn paste() to concat directory compoents

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/helpers.h

@@ -103,6 +103,17 @@ static inline int create(char *path, mode_t mode, uid_t uid, gid_t gid)
 	return 0;
 }
 
+/* paste dir/file into buf */
+static inline int paste(char *buf, size_t len, const char *dir, const char *file)
+{
+	if (!dir)
+		dir = "";
+	if (!file)
+		file = "";
+
+	return snprintf(buf, len, "%s%s%s", dir, fisslashdir(dir) ? "" : "/", file);
+}
+
 int	ismnt		(char *file, char *dir, char *mode);
 int	fismnt		(char *dir);