Log Message:
gegl: Update to 0.4.26

Changelog:
GEGL-0.4.26 2020-08-02
----------------------

Core:
~~~~~

Allow unsetting of property keys on paramspecs.

Operations:
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perlin-noise: use a local random generator, avoiding resetting the global one.
transform: decrease epsilon for affine-detection, and round some affine matrices \ 
to be exact.