Log Message:
Update to 0.4.8

Changelog:
GEGL-0.4.8 2018-08-17
---------------------

Core/GeglBuffer
~~~~~~~~~~~~~~~

Fixes to races during buffer/tile storage destruction, improve swap usage for
stored empty tiles.

Operations
~~~~~~~~~~

 motion-blur-circular - improve/clarify property ui
 median-blur          - added abyss-policy property
 long-shadow          - new operation
 little-planet        - adapt reference composition