Forcing splay to leg

[AndrewAkinson]

This overlaps a little with https://github.com/richsmith/sexytopo/issues/48

When a splay if forced to a leg this is fine. However, usually what happens is you take 3 readings and they do not quiet work, maybe when shooting up an avon. When forcing the 3 shots, Sexytopo treats each one as a new leg and issues a new number. It would be nice to do it intelligently, as Pockettopo does. In Pockettopo you still have to force them individually but it numbers them all the same.