The check-formats.c test depends on the exact format of the strings
returned from these functions, so add a test here.
a1-trap-test isn't the ideal place, but it seems like overkill to add
a new test just for these trivial checks.
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.