Update _util.py

Fixing missing import.
Merge pull request #303 from mnowotka/patch-1

Update _util.py
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Fix for #304: test for `str`, not `"utf-8"`.

The code wants to produce a `str` object for the given Python version (which is the right thing to do here).
Merge pull request #306 from mjpieters/master

Fix for #304: test for `str`, not `"utf-8"`.
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Add RGBA support to ImageColor
Fix imagecolor test issue
Added IGNORE_DECODING_ERRORS flag to ImageFile allowing corrupted images to load
Merge pull request #311 from cezarsa/master

Added IGNORE_DECODING_ERRORS flag to ImageFile allowing corrupted images to load
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Revert "Added IGNORE_DECODING_ERRORS flag to ImageFile allowing corrupted images to load"

This reverts commit 156a443cdf8e62ca8e942d024f9bcf212a12180b.
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Merge pull request #309 from yoavweiss/master

Add RGBA support to ImageColor
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Fix IOError when saving progressive JPEGs.

when the jpeg encoder sees the flags optimize or progressive (or progression)
it will write the full image in one shot.

The bufsize needs to be big enough to hold the entire image. The current heuristic
is that the entire compressed image will fit in width * height bytes, but this
heuristic is only applied to save operations with the flag "optimize" and not to
save operations with the flag "progressive".

This patch fixes this oversight.

(Btw, it will probably be a good idea to have a loop that retries with a bigger
bufsize in case this guess is not big enough.)
Merge pull request #313 from e98cuenc/progressive

Fix IOError when saving progressive JPEGs.
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