Ensure towers are at corners

[dhasenan]

Right now, we have walls with a tower not quite at what looks like the end of a wall.

What happens is, the angle between two walls is shallow enough. Like you have a 5:1 NE:N wall, and it ends with a NE exit. Then you have a 3:1 E:NE wall, and it starts with a NE exit. This looks strange.

There are two obvious ways of doing things:

• Detect apparent corners and nudge towers to those corners.
• Alter the line-drawing code to ensure that it begins and ends with the major angle.

[dhasenan]

Okay, third obvious way: require walls to adhere to specific angles. But that would be messy.