Golog.Interpreter: renamed function den to ast.

I think it's an abstract syntax tree which is returned by this function.
The old name was supposed to stand for `denotational', but I don't know
whether this makes sense.
SCR: fixed angles, typo in steering command

The manual is wrong about the `steering' command, it's actually `steer'.
The angles for the track laser sensors were wrong (missing minus signs).