> This should fix it I guess, and it's how we deal with unused return
> values elsewhere. I've considered using USE_ASSERT_CHECKING here, but it
> seems rather ugly with that. I'll wait for Emre's opinion ...
Assert() is the wrong thing to do in here. Drawn-perpendicular lines
may not intersect because of precision loss. We have to check it and
return NULL. There a few of those that we crash, or return garbage,
or get NULL and fail in DirectFunctionCall()s. The next patch
"line-fixes" fixes them.