[pygame] sForzando speed update

[Nat Budin <natb@brandeis.edu>]

Sorry about the lack of promised speed fix; I've been really busy all week.  
Here's the results of all my testing.

I checked out the code for CCScene; apparently it has a 
multiple-inheritance-ambiguity bug that causes it to use the draw function 
from Node instead of CCNode - great! I thought.  There's the source of all 
our speed difficulties.  Unfortunately, when I disambiguated the function, it 
actually resulted in a whole bunch of weird graphical mishaps because things 
were no longer being erased (a greivous omission in CCNode.draw, to be sure). 
 In addition, there was no speedup - in fact, there was a rather severe 
slowdown.  I fixed the no-erase problem, but that slowed things down even 
more (at this point things were about 25% slower than the original version).

I decided to go test on a slower machine.  The machine I tested on was a 
Pentium II-300 running Red Hat Linux 6.  To get some sort of honest figures, 
I added FPS measurement code to a PyGame example to see what kind of speed 
they ran at on this machine.  stars.py ran at about 20 FPS.  Then I ran 
dialog.py (0.1 beta before my recent changes).  Also 20 FPS.  Hmmmm.  Then I 
ran the changed version.  16 FPS - just about the expected 25% slowdown.

I really have no idea what's up at this point.  It seems like redrawing the 
whole screen every frame is actually FASTER than redrawing small bits of it 
that change.  I don't have a clue why.  There is one final optimization I 
want to make, which might result in some speedups.  Instead of flipping every 
frame, I am going to make sForzando use pygame.display.update to only update 
what is necessary.  This will probably speed things up a little, but don't 
expact huge performance increases.  Like I said, dialog.py runs slow on a 
slow machine, but so does stars.py.

Also coming soon from the sForzando front: sforzaliens.py, a fun little 
example to show how to add sForzando to existing games - in this case, we add 
a sForzando dialog on top of Pete's Aliens game, and show how it can be moved 
around and acts just like it does in a completely sForzando-based game.

Thanks to everyone who provided advice and support during the debugging 
process.

Nat
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