Include option that allows decreasing values for usage with solar panels

[hansbruy]

I have watermeter running to capture my electricity usage.
When my solar panels are generating power my electricity meters count backward, however watermeter does not take into account these (reduced) updated values (as they are lower than the last value and throw an error).

Requesting an option is added that would allow for decreasing values (within boundaries of max. threshold). So rather than checking "is new value larger than old value with threshold" it would be "is new value larger or smaller than old value with threshold.
This option should be configurable with the normal interface (config.php)