Remove implicit path completion - I didnt really want it and it was causing problems
   1) normalize-vector was blowing up when we were doing something on a zero length line. In that case the normalized vector is just 0 anyhow, so I returned a zero point(vector?) from point-/ if the line length is zero - this seems do do the right thing and keep it from crashing

    2) cicrle-through-3-points was blowing up on degenerate input.

     when two of the points were the same thing (or had an x or y value that were the same), it would crash with a /0 error. The point-equal items at the top filtered out any degenerate input in the data I had, but should probably be fixed to rule out anything that will cause a /0 crash.

    In the case of degenerate input (i.e. if we have a control point that is at the same spot as the beginning or ending point on the bezier) - this wont work for biarc, so I return a nil which forces the algorythm to use the midpoint of bezier method rather that biarc. This works fine.
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