[rms] Misplaced ordering when dropping document into presentation trail

[geireann]

When I dragged the document on Supervenience into the presentation trail at the bottom of the stack, it should have been the bottom but instead put it into the place above the last item in the trail. I have a movie of this that I can email out - github doesn't support movies as files

[geireann]

Noted

[bobzel]

fixed