If you compile simutrans with ONLY_TUNNELS_BELOW_GROUND you aren't able to build tunnels anymore. This is fixed with this patch.
The patch als fixes the bug displayed in the attached image (you can build a tunnel if the ending tile contains a way but no slope).
Building a tunnel to a vertical slope was once a hidden feature though ...
Will ONLY_TUNNELS_BELOW_GROUND work well with current version ?
Now it's time to activate this as default, isn't it ?
yes, I am all for deactivating the harbour tunnels. At least, since rev. 2547 tunnels through open water are forbidden.
???
But I can still build it in r2550.
(http://simutrans-germany.com/files/upload/z_slope4.png)
This is 'intended'. I meant tunnels under sea level into the sea, as in here:
http://forum.simutrans.com/index.php?topic=2549.0
As soon as the slope building is working on all levels as intended, harbour tunnel should be disabled. I think so too. But then we need to improv all Undergrund modus (maybe with transparent sea tiles)