moved door creation into CreateOneStep

[Rushwind13]

This is an attempt to get hallways to "link up" with each other -- I hardly ever see long hallways in the current build algorithm.

Two known problems:

• edge checking will "fail" if a hallway extends into an existing room or hallway (this should be allowed)
• many "off by one" or "off by two" errors -- two lit hallways terminating next to each other, or "looks like a secret door" -- but isn't.