[sungbin1015]

Follows on from #10242.

Changes proposed in this pull request:

• Round crop coordinates ending in .5 up, instead of to the nearest even integer
• Add test_crop_float_half
• Add a 13.1.0 release note

_crop() uses round(), which since Python 3 sends halves to the nearest even integer. So the same box can come out a pixel larger or smaller depending on where it is:

from PIL import Image

im = Image.new("L", (200, 10))
for left in (84.5, 85.5):
    print(im.crop((left, 0, left + 31, 1)).size)
print(im.crop((1.5, 0, 2.5, 1)).size)

(32, 1)
(30, 1)
(0, 1)

With math.floor(v + 0.5) these are (31, 1), (31, 1) and (1, 1). Coordinates that aren't exactly .5 round as before, so test_crop_float from #1745 is unchanged. #10229 is close in spirit, but it changes how ImageDraw truncates negative coordinates in C and doesn't touch crop().

The full test suite and pre-commit pass locally.