Set FULL_SCREEN_HEIGHT to 25 instead of being cute

The Tiles and Win32 builds do just this (i.e. set it to 25) regardless of the effective size, but those have special handling anyway -- they may just always have an odd-height "terminal" to display in.

On the other hand, doing this doesn't seem to have broken anything, and it really did seem a little odd otherwise:
![bad-veh-interact](https://f.cloud.github.com/assets/591573/1605651/33e76518-53e3-11e3-8a9e-cf53f9f7893f.png)

Bad vehicle-interact window, no cookie!