correctly check for fixes that maintain their own pressure compute

  int ipress = modify->find_compute(id_press);

  c_press = modify->compute[ipress];

  // Check if nh type fixes have been called

  // See comment in the setup method

  for (int i = 0; i < modify->nfix; i++) {

    if ( strncmp(modify->fix[i]->style,"nph",3) ||

         strncmp(modify->fix[i]->style,"nph_sphere",10) ||

         strncmp(modify->fix[i]->style,"npt",3) ||

         strncmp(modify->fix[i]->style,"npt_sphere",10) )

      error->all(FLERR,"Fix plumed must be called before fix_nh derived fixes, "

                 "for instance nph and npt fixes");

    const char * const check_style = modify->fix[i]->style;

    // There must be only one

    if (strcmp(check_style,"plumed") == 0)

      error->all(FLERR,"There must be only one instance of fix plumed");

    // Avoid conflict with fixes that define internal pressure computes.

    // See comment in the setup method

    if ((strncmp(check_style,"nph",3) == 0) ||

        (strncmp(check_style,"npt",3) == 0) ||

        (strncmp(check_style,"rigid/nph",9) == 0) ||

        (strncmp(check_style,"rigid/npt",9) == 0) ||

        (strncmp(check_style,"msst",4) == 0) ||

        (strncmp(check_style,"nphug",5) == 0) ||

        (strncmp(check_style,"ipi",3) == 0) ||

        (strncmp(check_style,"press/berendsen",15) == 0) ||

        (strncmp(check_style,"qbmsst",6) == 0))

      error->all(FLERR,"Fix plumed must be defined before any other fixes, "

                 "that compute pressure internally");

  }

}