All the tests are linked to libutil, hence it makes sence to always
include utils.h and reuse what it provides (config.h inclusion, access
to private pixman APIs, ARRAY_LENGTH, ...).
When a trapezoid sample point is exactly on a polygon edge, the rule
is that it is considered inside the trapezoid if the edge is a top or
left edge, but outside for bottom and right edges.
This program tests that for a1 trapezoids.
