The `Greiner-Kai` phase 2 mentions: `if P0 inside other polygon` (Figure 12).
removing dead code.
adding more unit tests.
modifying the values used for clip2.
this goes along with a previous commit.  Since we fixed phase 2, we can fix phase 3.

In phase 2, the `status_entry` was being initialized using the wrong polygon.
point to a working version of the `polygon` library.  Otherwise the unit tests won't work.