GIMP 2.8.20

Core:
- Avoid D-Bus error message when built without D-Bus support
- fix OS X min required conditional in gimpimagewindow.c
- Saving to existing .xcf.bz and .xcf.gz files didn't truncate them
  and could lead to unnecessarily large files
- Text layer created by gimp-text-fontname doesn't respect border
  when resized
- avoid seeking when saving XCF files to prevent corruption with
  file network shares (fixed since 2014, but not mentioned in NEWS yet)

GUI:
- Flow on Paint Dynamics editor dialog: the 'y' axis is indicating
  'Rate' instead 'Flow'
- Vertical ruler shows artifacts if the status bar isn't showing
- Tablet stylus misbehaves when crossing the edge of a dock in
  multi-window-mode
- Disable the new "automatic window tabbing" feature introduced on macOS
  Sierra
- Improve the visiblity of slider handles with dark themes
- Make it harder to switch to renaming if selecting already selected
  items in resource lists

Tools:
- make toggling to color picker mode of paint tools more robust

Libgimp:
- call gimp_file_entry_set_filename() with filename encoding

Windows Installer:
- Reduce the memory requirement when running the installer (has
  already been shipped in a 2.8.18 installer-only update)
- Ship an updated libcairo to fix GTK+ UI rendering problems, like
  missing palette border/bevel and shadowa under tab labels

macOS DMG:
- Ship the Tango icon theme with the DMG for a complete set of icons
- fix the way mime data is copied into the bundle
- no longer copy Pango modules into the bundle
- prevent a crash caused by drag&drop on OSX by patching the included
  GTK+
- ship a patch for gettext to make sure the preferred UI language
  will be used

Plug-ins:
- Prevent the Python console from closing by the Escape key
- Help browser does not launch on OS X
- Filter 'Edge Detect/Difference of Gaussians' returns empty image
- only use -xobjective-c for compile commands
- mkgen.pl: fix calls to write_file() routine to write to current
  directory
- When printing, the images are composed onto a white background to
  prevent printing a black box instead of a transaprent image
- Fix color visison deficiency display filters to apply gamma
  correction directly

(adam)