epsilon3 and intersect(a, b)

[Fil]

From Jason Davies's code (ported in 82d9481#diff-1955ba130f17ffd3f1a5db97ee798e02R13 ), there was an epsilon2 test in this function.

Somehow it allowed lines to escape the clipping on some occasions, so I lowered it to epsilon3 in 202e604 and got much less errors.

But it still happens, and the fix is to get rid of any epsilon and compare the values with 0.

I wonder what I'm missing (in which cases this value should be st. positive), but testing in all my examples seems to be OK with 0 instead of epsilon3.

[Fil]

Now this creates a random error in the d3-geo-projection tests: sometimes they give the exact image, and sometimes not (in different runs).

The difference between those images and the reference is so tiny only the test sees them. (Red dots on the top-left edge).

[Fil]

A way to get reproducible results and avoid the tests wobbling is to get rid of Math.random() and replace it with a deterministic function like Math.sin( 10000 * xxx). Fix coming soon