T-Junctions and Y-scaled flat primitives in the Library Spec

[Orion Pobursky]

T-Junctions:
These are discouraged in the file format spec:

Where possible, abutting polygons should share common verticies.

I'd like to explicitly disallow in the library spec.

Y-scaled flat primitives:
These are not mentioned in the file format spec or the library spec.
I'd like to explicitly disallow in the library spec.