2-edge HIDDEN_JUNCTION: hidden system & region split compatibility

[yakra]

https://forum.travelmapping.net/index.php?topic=4781.msg36042#msg36042

VISIBLE_HIDDEN_COLOC are naturally going to occur on border points,
with [ITA-LOM A1 LOM/EMI] colocated with [ITA A1 +LOM/EMI].

This affects 2-edge HIDDEN_JUNCTION cases too. As-is, this yields 166 FPs.
Easy fix: HighwaySegment::same_routes -> HighwaySegment::same_con_routes.
Requires minor changes to 4 lines of code.

I've made the changes locally, but will include with hidden system implementation to avoid a merge conflict.
Easy enough. Just leaving this reminder to remember to do that.

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Thankfully, leaving in easy access to some debug text made it easy to spot what was going on.