Eric Agol

@giordano Thanks for the suggestion, Mosé! It did turn out that pre-allocation was causing most of the slow down. Also found some other improvements which match C speed in this...

@dmhernan Yes, and not a feature I am fond of...

When I change this to `TRANSIT_TOL = 10*sqrt(eps(one(typeof(h))))`, this causes the numerical derivatives in `test_findtransit2` to no longer pass. This is strange behavior, but could be due to the acceleration...

I decreased the tolerance, but the discrepancy continues. Indeed, it turns out that `gdot` is being computed inaccurately, due to a slight difference between `v` and `dx/dt`.

To resolve this I need to compute `dq/dtq` which I never got working properly.

I got the computation of `dq/dt` working with `dh17` which involved assigning `jac_step` to the identity just before `phisalpha`. This routine still isn't working in the `kick fast` limit, but...

They do not - but don't differ by much.