Give error if data_dir exists but is a file.

src/main.rs

@@ -78,7 +78,12 @@ fn main()
 		Err(_e) => PathBuf::from("./"),
 	};
 
-	if !data_dir.exists()
+	if data_dir.exists() && data_dir.is_file()
+	{
+		panic!("Error: {} file already exists! Please (re)move it.",
+			data_dir.display());
+	}
+	else if !data_dir.exists()
 	{
 		println!("Creating {} data directory.", data_dir.display());
 		fs::create_dir_all(data_dir)