clone: more forcefully clean clones of untracked files and empty dirs

ofborg/src/clone.rs

@@ -137,6 +137,16 @@ pub trait GitClonable {
             .stdout(Stdio::null())
             .status()?;
 
+        debug!("git clean -x -d --force");
+        Command::new("git")
+            .arg("clean")
+            .arg("-x")
+            .arg("-d")
+            .arg("--force")
+            .current_dir(self.clone_to())
+            .stdout(Stdio::null())
+            .status()?;
+
         lock.unlock();
 
         Ok(())