code: public String getWikiUrl(String filePath) {
          String wikiUrl = null;
          String filesDir = getFitNesseFilesSectionDir();
          if (filePath.startsWith(filesDir)) {
              String relativeFile = filePath.substring(filesDir.length());
              relativeFile = relativeFile.replace('\\', '/');
              wikiUrl = "files" + relativeFile;
          }
          return wikiUrl;
      }
docs: Converts a file path into a relative wiki path, if the path is insides the wiki's 'files' section.
  @param filePath path to file.
  @return relative URL pointing to the file (so a hyperlink to it can be created).