gegl: don't leak the swapdir in gegl_config_set_defaults()
gegl: don't leak GeglConfig:application_license on exit
edge-sobel: add doc-description to keep_signal property
edge-sobel: mark description added in prev commit for translation
sobel: Rename property keep_signal to keep_sign
sobel: Clean up the implementation

This implementation also makes the result compatible with the classic
GIMP plug-in.
sobel: Add comment
sobel: Code style, etc.
sobel: Simplify buffer usage by clamping
sobel: Bring OpenCL implementation closer to the C one

There is still the case of removing the sobel radius and access out
of rect bounds.
sobel: Match classic GIMP behavior more closely
Catalan translation
warp: restore indentation after search and replace of GeglProperties
png-load: Port to GIO, add 'uri' property

Allows loading PNG files from any uri scheme supported by GIO/GVFS,
including HTTP, SMB, FTP etc.
Note: Currently does not support stdin (path='-')
png-load: Refactor stream handling to avoid reading twice

Also moves some things out to dedicated functions and adds
GError based error handling.
tests/compositions: Print exception if VERBOSE
png-load: Add back code for reading from stdin

Was temporarily missing after GIO refactor. Can now read stdin
again, but the functionality is broken: get_bounding_box()
eats some of PNG files, so process() sees an incomplete file.
This bug was there before also.
Includes an implementation for WIN32, but I have no idea if it compiles.
gegl-xml: When failing to resolve absolute path, pass raw input
png-load: Only print error on error

On EOF read_all() will return FALSE and possibly less-than-requested bytes
png-load: Move function for opening stream to library

In order to be able to reuse it in the other file loaders,
like gegl:jpg-load.
In private header for now.