code: synchronized void unreserve(ChangedFile changedFile) {
          ChangedFile removedFile = this.reservedFiles.remove(getKey(changedFile));
          if (removedFile != null && !this.fileList.containsKey(getKey(removedFile))) {
              addChangedFile(removedFile);
          }
      }
docs: Releases the reservation on the file (if still reserved) and returns
  it to the list.
  
  @param changedFile