[Etoys] Performance improvements form 3.9 (backported) #1

[Yoshiki Ohshima]

  Marcus,

  Thank you for sending these.  I made up two images (based on #1059)
with and without these changes and measured performance on the A-test
board.  Here are the numbers from three measurements each:

without:
'#1059 memory=19310712 display=1012x700x16 painter=1483.2 viewer=1802.4 scriptor=1487.2 category=2628.8 ' 
'#1059 memory=19228056 display=1012x700x16 painter=1478.4 viewer=1796.8 scriptor=1470.4 category=2625.2 ' 
'#1059 memory=19022612 display=1012x700x16 painter=1565.2 viewer=1803.8 scriptor=1468.4 category=2627.0 '

with:
'#1059 memory=19322540 display=1012x700x16 painter=1540.2 viewer=1701.4 scriptor=1428.8 category=2449.2 ' 
'#1059 memory=19239884 display=1012x700x16 painter=1523.2 viewer=1691.2 scriptor=1411.2 category=2446.8 ' 
'#1059 memory=19030604 display=1012x700x16 painter=1605.8 viewer=1701.4 scriptor=1401.6 category=2460.8 '

  Other than "painter", we get several percent points improvement.
Pretty good.

  I'm a bit puzzled to see the performance degragation in "painter"...
Probably I should try different combinations of these changes, but at
this piont, I'd push all to the update stream.

  Thank you so much!

-- Yoshiki