docs: protected Collection<File> extractDependentLibs(final File cachedir) throws IOException {
          final Attributes attributes = getMainAttributes();
          if (null == attributes) {
              debug("no manifest attributes");
              return null;
          }
  
          final ArrayList<File> files = new ArrayList<File>();
          final String libs = attributes.getValue(RUNDECK_PLUGIN_LIBS);
          if (null != libs) {
              debug("jar libs listed: " + libs + " for file: " + pluginJar);
              if (!cachedir.isDirectory()) {
                  if (!cachedir.mkdirs()) {
                      debug("Failed to create cachedJar dir for dependent libs: " + cachedir);
                  }
              }
              final String[] libsarr = libs.split(" ");
              extractJarContents(libsarr, cachedir);
              for (final String s : libsarr) {
                  File libFile = new File(cachedir, s);
                  libFile.deleteOnExit();
                  files.add(libFile);
              }
          } else {
              debug("no jar libs listed in manifest: " + pluginJar);
          }
          return files;
      }