world_region_feature.unk_30 may be cavern lake indicators

[PatrikLundell]

According to Rekov (see http://www.bay12forums.com/smf/index.php?topic=164136.msg8306462#msg8306462) world_region_feature.unk_30 (in df.world-data.xml) may be a field controlling cavern lakes. The thread post should cover the info in all details except the field referenced (which is provided here).

I haven't looked into it further, but add it as an issue here to reduce the risk of it being forgotten.

[quietust]

Looking at the Toady headers, it appears that these flags have multiple meanings depending on what kind of features are inside.

For River features, there are two flags "SOURCE" and "SINK".

For Layer features (i.e. caverns), there are 4 flags "LIQUID_U", "LIQUID_D", "LIQUID_L", and "LIQUID_R".