code: private boolean isUniqueFileResolved(final Set<String> alreadyHandled,
        final String s) {
      return this.uniqueFiles && alreadyHandled.contains(s);
    }
docs: Examines a source file whether it is already resolved when it should be
  unique.
  
  @param alreadyHandled
  all source files already resolved
  @param s
  source file to resolve
  @return true if source files should be unique and the source file already
  resolved