Fencepost error in checking stability_last_downrated results in double calls to rep_hist_downrate_old_runs()

Check out this code in rep_hist_downrate_old_runs() in src/feature/stats/rephist.c:

  if (stability_last_downrated + STABILITY_INTERVAL > now)
    return stability_last_downrated + STABILITY_INTERVAL;

  /* Okay, we should downrate the data.  By how much? */
  while (stability_last_downrated + STABILITY_INTERVAL < now) {
    stability_last_downrated += STABILITY_INTERVAL;
    alpha *= STABILITY_ALPHA;
  }
[...]
 return stability_last_downrated + STABILITY_INTERVAL;

Ok, so we tell it to call the function next when now == stability_last_downrated + STABILITY_INTERVAL. But the first check above is >, and the second check is <.

This results in double-calls each 12 hour period, where the first call uses an alpha of 1.0:

May 15 23:48:13.752 [info] rep_hist_downrate_old_runs(): Discounting all old stability info by a factor of 1.000000
May 15 23:48:14.752 [info] rep_hist_downrate_old_runs(): Discounting all old stability info by a factor of 0.950000
May 16 11:48:13.753 [info] rep_hist_downrate_old_runs(): Discounting all old stability info by a factor of 1.000000
May 16 11:48:14.752 [info] rep_hist_downrate_old_runs(): Discounting all old stability info by a factor of 0.950000

As far as I can tell, the call with alpha at 1.0 is harmless? I think?

And I guess that the fix is to turn the < into a <=.