[issue21597] Allow turtledemo code pane to get wider.

[Lita Cho]

Lita Cho added the comment:

Hi Terry!

> 2. More important: when I move the slider right, the text widen and the canvas narrows relatively smoothly. 

This is not due to the mixing of Pack and Grid Managers. This is due to adding Frames within a Pane Window. If I just create two empty Pane Windows, I don't get the lag. However, if I add a Frame container within Pane Window, I do. I've tried switching between using only the Pack Manager and then again using only the Grid Manager. However, that lag still exists. 

I have the code here if you want to try the packed version.

```
from tkinter import *
root = Tk()
m = PanedWindow(root, orient=HORIZONTAL, sashwidth=10)
rightF =  Frame(m)
leftF = Frame(m)
top = Label(leftF, text="lefgt pane", bg='blue')
bottom = Label(rightF, text="right pane", bg='red')
top.pack(fill=BOTH, expand=1)
bottom.pack(fill=BOTH, expand=1)
m.add(leftF)
m.add(rightF)

m.pack(fill=BOTH, expand=1)
mainloop()
```

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue21597>
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