Sort ids when restricting to maxNumEntries with degenerate counts

[constantinpape]

The current implementation keeps arbitrary ids when restricting the entries in a multiset to maxNumEntries if the counts are degenerate. It would make it easier to compare implementations if it would sort the degenerate ids in ascending order instead.
For example, the current implementation yields the result ids: [303 310 315], counts: [156 147 77] when summarising a label array with ids: [303 306 310 311 315], counts: [156 55 147 77 77] with maxNumEntries=3. I would expect to obtain ids: [303 310 311], counts: [156 147 77]instead.

For this change, one would only need to change the comparison here, I think.