Improve ladder placement

[Oblomov]

Ladders placed against other ladders while sneaking will copy the
existing ladder's param2, thus allowing vertical construction even in the absence
of walls behind them.

[paramat]

MTG is feature-frozen so we might not be able to accept this.

[rubenwardy]

I thought it was just gameplay feature frozen, and maintenance is fine?

[Wuzzy2]

 	if sneaking and under and under.name:find("^default:ladder_") then

No, just no.

[sfan5]

The approach is not very portable, but stairs also does this and given that there are exactly two ladder nodes in MTG I don't see the issue.

[appgurueu]

The approach is not very portable, but stairs also does this and given that there are exactly two ladder nodes in MTG I don't see the issue.

Groups should be used, both for stairs and for this.