fix storage size for internal compute ids in fix plumed

  // Define compute to calculate potential energy

  id_pe = new char[7];

  id_pe = new char[8];

  strcpy(id_pe,"plmd_pe");

  char **newarg = new char*[3];

  newarg[0] = id_pe;

  // Define compute to calculate pressure tensor

  id_press = new char[9];

  id_press = new char[11];

  strcpy(id_press,"plmd_press");

  newarg = new char*[5];

  newarg[0] = id_press;