There is a new addon in the repository: v.net.curvedarcs.
https://grass.osgeo.org/grass72/manuals/addons/v.net.curvedarcs.html
It is a frontend to v.net and v.segment that creates curved arcs between given start and end points, thus allowing to display flows (or relations) between points while avoiding overlaps of lines.
Enjoy !
Moritz