Overflow when saving certain areas at 40X

[nathanin]

Might have to change the strategy for saving from high resolution slide.

Hangs for a while then:

Traceback (most recent call last):
  File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 1540, in __call__
    return self.func(*args)
  File "imageLoadGUI/ImageLoadGUI.py", line 326, in buttonCropOK
    self.SaveImg()
  File "imageLoadGUI/ImageLoadGUI.py", line 350, in SaveImg
    out = self.image.SVS.read_region(corner, level, size)
  File "/usr/lib/python2.7/dist-packages/openslide/__init__.py", line 219, in read_region
    level, size[0], size[1])
  File "/usr/lib/python2.7/dist-packages/openslide/lowlevel.py", line 223, in read_region
    return _load_image(buf, (w, h))
  File "/usr/lib/python2.7/dist-packages/openslide/lowlevel.py", line 62, in _load_image
    return PIL.Image.frombuffer('RGBA', size, buf, 'raw', 'RGBA', 0, 1)
  File "/usr/lib/python2.7/dist-packages/PIL/Image.py", line 2117, in frombuffer
    core.map_buffer(data, size, decoder_name, None, 0, args)

MemoryError: Integer overflow in ysize