The four remaining "classic" color tools (Brightness-Contrast, Curves,
Levels and Threshold) are in fact just special UIs for otherwise
completely normal filter ops.
Add normal filter actions for them and invoke them like all
other filters, which makes them show up in the filter history
automatically.
The only small hack needed is to special case them in
gimp_gegl_procedure_execute_async() so the right tools are created
instead of the default GimpOperationTool. Also, blacklist the
automatically generated tools actions from action search and the
shortcut editor.
so the threshold can now be based on the GimpHistogramChannel enum.
Add a channel menu to the threshold dialog and a channel argument to
the PDB procedure (which is new in 2.10).
If I hadn't forgotten what the "RGB" channel is supposed to do I would
have implemented the RGB mode in GimpOperationThreshold correctly.
Right now I'm just guessing. Anyone?
- don't include <gdk-pixbuf/gdk-pixbuf.h> in headers in app/
- instead, include it in many .c files instead of <glib-object.h>,
finally acknowledging the fact that app/ depends on gdk-pixbuf almost
globally
- fix up includes as if libgimpbase depended in GIO, which it soon will
