[TYPO3-core] RFC #8878: Bug: Fix cropscale behaviour for transparent GIF

[Felix Buenemann]

This is an SVN patch request.

Type: Bugfix

Bugtracker references:
http://bugs.typo3.org/view.php?id=8878

Related:
http://bugs.typo3.org/view.php?id=8763

Caused by:
http://bugs.typo3.org/view.php?id=8025

Branches:
TYPO3_4-2, TYPO3_4-3, TYPO3_4-4, trunk

Problem:
When using cropscale on an image with transparent background, the 
parameters for cropping differ between im4 and im6, due to how they 
handle the transparent canvas. This leads to incorrect cropping when 
using im5 or im6.

Solution:
Adapt behaviour according to im_version_4 flag and revert to pre #8025 
behaviour when im5/6 are used.

Notes:
A short testcase ts code and sample image can be found in the bug 
report. Picture that illustrates problem attached.

Best Regards,
    Felix Buenemann
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