PCSCALE is irrelevant when units are used

[ajkeller34]

The PCSCALE factor used to integrate with Clipper is actually harmful when units are used.

It is necessary when no units are used so that values to the right of the decimal point are not neglected. Without units, you have no idea how many decimal points will actually matter in the output GDS file, because the database unit is not known at the time of polygon clipping.

Short-term solution: If you encounter problems, provided you use units, set this constant to 1.0.

Suggested long-term solution: remove support for unitless coordinates.

cc @eunjongkim @mtfang

[ajkeller34]

cc @vtdsferreira