Exercise trailing comma in tuples.

Fixed center().
Rewrote ljust() and rjust().

Automatically call self.destroy() if WE_CLOSE event dispatched.
Added keyboard, alternate drawing and getwindow interface.
Call child's realize method.

(why not keyboard?)

Made more functions externally visible.

optimization.

Fixed 'needspace' hack to use a flag in the stdout file object;
added local and global variable lookup cases.