[Therion] Setting -outline for pit lines

[Tarquin Wilton-Jones]

> You may not specify attribute -outline in case of pit. 

Why not? It is perfectly normal for a passage to end at a pit, and that
pit therefore becomes a line that terminates a passage.

I have attached a hand drawn example of how this would appear normally
on a plan view (at least, this is how it would normally appear on a plan
survey in the UK, such as the survey of a pothole - vertical cave - like
Swinsto or Simpson's).

"-outline in" does work on the pit line here for generating a PDF. But
shows a warning when generating LOX.
"-outline out" also works without a warning when generating LOX or when
generating PDF.

What I don't understand is

1. Whether "-outline out" is actually the correct thing to use when the
pit line points outwards rather than inwards.

2. Why it even matters which way we draw a *wall*, if "outline out"
always can pick the "correct" side to fill. Surely if it can work out
the "correct" side of a pit line, it can also work out the correct side
of a "wall" line, and it doesn't even matter whether the yellow tick
points towards "air" or "rock".

(Having to have an invisible wall on the lower scrap makes complete
sense to me though, since that has to have a curved wall matching the
curve of the pit line above. This is what I already use.)
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