Allow rail signals closer together

[sparr]

factorio_signals_too_close.png (331.08 KiB) Viewed 246 times

Here we have two signals on the top rail that produce distinct breaks in the rail blocks.

The signals on the middle and bottom rail produce the same breaks, but aren't allowed to be placed on the same rail.

[sparr]

Placing two signals adjacent that DON'T produce distinct rail block break locations would be a different use case. Perhaps that would still be illegal. Perhaps it would produce a zero-length block. Perhaps it would be handled as a new case. This is the case that's more relevant to tiling blueprint creation, but also the more complex case.