inkscape: Current supported version of inkscape only support python2.

And upgrading to the python3-supported version (1.1) requires gtk3 and recent
versions of freetype, glib, atk, gtk, gtkmm, atkmm...

https://wiki.inkscape.org/wiki/Tracking_Dependencies

component/inkscape/buildout.cfg

@@ -23,6 +23,8 @@ extends =
   ../popt/buildout.cfg
   ../xorg/buildout.cfg
   ../zlib/buildout.cfg
+# Inkscape < 1.1 only supports python2
+  ../python-2.7/buildout.cfg
 
 [gsl]
 recipe = slapos.recipe.cmmi
@@ -52,7 +54,7 @@ configure-options =
   -DWITH_LIBVISIO=OFF
   -DWITH_LIBWPG=OFF
 environment =
-  PATH=${cmake:location}/bin:${freetype:location}/bin:${gdk-pixbuf:location}/bin:${gettext:location}/bin:${glib:location}/bin:${intltool:location}/bin:${libxml2:location}/bin:${pango:location}/bin:${perl:location}/bin:${pkgconfig:location}/bin:%(PATH)s
+  PATH=${cmake:location}/bin:${freetype:location}/bin:${gdk-pixbuf:location}/bin:${gettext:location}/bin:${glib:location}/bin:${intltool:location}/bin:${libxml2:location}/bin:${pango:location}/bin:${perl:location}/bin:${pkgconfig:location}/bin:${python2.7:location}/bin:%(PATH)s
   PKG_CONFIG_PATH=${:pkg_config_depends}
   CMAKE_INCLUDE_PATH=${boost-lib:location}/include:${freetype:location}/include:${garbage-collector:location}/include:${libjpeg:location}/include:${lcms2:location}/include:${libpng:location}/include:${zlib:location}/include
   CMAKE_LIBRARY_PATH=${boost-lib:location}/lib:${freetype:location}/lib:${garbage-collector:location}/lib:${lcms2:location}/lib:${libjpeg:location}/lib:${libpng:location}/lib:${zlib:location}/lib