fix editmap derp

This is a branch from atomicdryad, that fixes a serious bug in the overmap terrain debug menu. That bug prevents users from debugging things like the new dojo. Currently editmap uses the terrain list instead of the overmap terrain list. Because that terrain list is shorter it does not cause any crashes, but it hides many overmap terrains (.., dojo).

I didn't found this, atomicdryad did. He/she should be complimented, but I thinks this should really go into the mainline. I don't know the policy of those things, so please excuse me if this is the wrong way to handle it.