src/utils_threshold.c: Implement the “Hits” and “Hysteresis” config options.

src/utils_threshold.c: Implement the “Hits” and “Hysteresis” config options.

Hi all!

Based on Mariusz's idea, i attach a patch for thresholds (no for
filtering, yet) with basic hysteresis support adding the keyword
Hysteresis to configuration file, for example:

<Threshold>
  <Type "load">
     DataSource "midterm"
     WarningMax 1
     Hysteresis 0.3
  </Type "load">
</Treshold>

In this case the notification is raised when load (midterm datasource)
is greater than 1, and came back to OKAY when lower than 0.7 (1 - 0.3).

This is a proof of concept and I do not have a lot of time to test,
please use this patch with caution. Furthermore, the code is really hard
and dirty :)

Best regards,
  Andres

P.S.: The patch also including hits support, so to compile you also
require to apply hits-cache.patch and, obviously this patch is
incompatible with hits-threshold.patch.

Signed-off-by: Florian Forster <octo@leeloo.lan.home.verplant.org>