Bug-- Tunnels are counted with powerline maintenance

[Fifty]

Noticed this in pak 64 112.3 and it still exists in nightly r6550. Maintenance costs in the powerline tab seemed very high, and then I realized that players without powerlines at all had maintenance costs for them 

After some testing, I realized that tunnels were the culprit: both road and rail tunnels have their maintenance costs counted under powerlines, even though their construction costs go under the road or rail headers. For whatever reason, you need to build the tunnels, and then save and reload the game for Simutrans to start showing the bug; it is correctly listed when first built.

Kudos to everyone involved in the finance patch, it's a really great addition!

[TurfIt]

r6554 should fix.