Better handling of data entry settings

[altenbach]

For non-integer increments, the data entry currently accumulates binary errrors due to the limits if the DBL representation, so e.g. sometimes the upper limit cannot  be reached using the increment button several times, but only when entering the upper limit directly.

This comes up at regular intervals, e.g. here. In one fo these discussions, I long ago suggested to make it into an idea. It seems this has not happened, so here it is! 🙂

This limitation needs to be handled with some internal code, e.g. to coerce the value to the nearest decimal fraction based on the least significant digit of the increment value whenever the up/down buttons are used. ... or something similar. 😉