Added group keywords to fix gcmc

  delete [] idshake;

  if (ngroups > 0) {

    // calling 2d destructor

    memory->destroy(groupstrings);

    for (int igroup = 0; igroup < ngroups; igroup++) 

      delete [] groupstrings[igroup];

    memory->sfree(groupstrings);

  }

  if (ngrouptypes > 0) {

    memory->destroy(grouptypes);

    memory->destroy(grouptypebits);

    // calling 2d destructor

    memory->destroy(grouptypestrings);

    for (int igroup = 0; igroup < ngrouptypes; igroup++) 

      delete [] grouptypestrings[igroup];

    memory->sfree(grouptypestrings);

  }

}