Fix GreensFun/evaluation.jl Hacks

[dlfivefifty]

Just multiplying the length of the function in logkernel by 2 is a horrible hack

[MikaelSlevinsky]

It's meant to overcome the Nyquist rate of something that might oscillate twice as fast; this assumes that the fundamental solution and the density have the same wavenumber. It's only been tested on simple geometries so far, not with curves. Multiply by 3? 😄

This is part of what makes it "fast," though this may be obsolete with GPU evaluation. An alternative is running each evaluation point through the constructor and standard chop.