Update to 0.4.12

Changelog:
GEGL-0.4.12 2018-10-23

GeglBuffer
~~~~~~~~~~

Fix fix of scaled blitting, the fix from last release introduced scaling
artifacts for all formats that are non-8bit.

Contributions to this relase
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Ell, Øyvind Kolås and Rodrigo Lledó

GEGL-0.4.10 2018-10-16
----------------------

GeglBuffer
~~~~~~~~~~

Fix integer overflow issues for u32 blit scaling code paths.

Reduced memory clearing overhead for temporary buffers during blit.

Round alpha component during u8 bilinear/box filtering (this caused artifacts
on OSX through interaction without unknown platform differences in
libc/compilter/graphics stack)

gegl_buffer_dup now matches source buffer abyss, shift and tile-size more
closely.

Added GEGL_TILE_COPY command for backends, for more efficient buffer
duplication/copies.

New GeglBufferIterator API.

Move type-generic scaling algorithms to GeglBuffer folder, move opencl
integration bits out of buffer.

Operations
~~~~~~~~~~

gif-load: new operation for decoding GIF images/animations, with frame delay
exposed as an out-property.

exr-save: do not hard-code a version name space
long-shadow: add 'Fading (fixed length)' style with a new user-defined
'Midpoint' parameter

maniuk06: use double precision, permitting to work on larger images.

watershed-transform: improved description

unsharp-mask: permit std-dev radius of up to 1500px (from 300).

Updated all operations to use new iterator API

Contributors to this release
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Alexandre Prokoudine, Anders Jonsson, Debarshi Ray, Ell, Hussam Al-Tayeb, Marco
Ciampa, Massimo Valentini, Øyvind Kolås, Piotr Drąg, Rodrigo Lledó and Tim
Sabsch.

(ryoon)