A bunch of geom tests fails without fp due to precision issues

[jdahlstrom]

The results are all correct, just need to be compared with a larger epsilon.

failures:
    core/src/geom.rs - geom::Plane3<B>::from_point_and_normal (line 361)
    core/src/geom.rs - geom::Plane3<B>::from_points (line 336)
    core/src/geom.rs - geom::Plane3<B>::new (line 313)
    core/src/geom.rs - geom::Plane3<B>::normal (line 382)
    core/src/geom.rs - geom::Plane3<B>::offset (line 398)
    core/src/geom.rs - geom::Plane3<B>::signed_dist (line 462)
    core/src/geom.rs - geom::Tri<Vertex3<A,B>>::normal (line 214)
    core/src/geom.rs - geom::Tri<Vertex3<A,B>>::plane (line 236)