paste_in_new_window.png consists of white lines on black ("Hermann illusion")
with a transparent rectangle in the middle.

Use this to test "Edit / Paste in New Window".

Prior to 2007-10-07, a troublesome sequence of steps with this image was:

1. Set the selection transparency mode to Transparent
2. Select All (Ctrl+A)
3. Copy (Ctrl+C)
4. Paste in New Window (Ctrl+Shift+V)

The white lines became transparent.

This testcase was originally by Thurston Dang.