This new test is derived from radial-test.c and displays conical
gradients at various angles.

It also demonstrates how PIXMAN_REPEAT_NORMAL is supposed to work when
used with a gradient specification where the first stop is not a 0.0:
In this case the gradient is supposed to have a smooth transition from
the last stop back to the first stop with no sharp transitions. It
also shows that the repeat mode is not ignored for conical gradients
as one might be tempted to think.