mergeNonWordSentences should give precedence to preceding, rather than following, children

[wooorm]

If L840 would use a minus operator, and L851 a plus operator, things like full-stops delimited by spaces (ellipses) would glue to their previous sentence (currently one full-stop glues to the previous, then a white space between sentences, followed by a new sentence, starting with two full-stop-space sequences).

I can’t however think of other use cases—though their probably are many more (like #1).