Replying to myself:I found the solution to the font msg here.And the pixbuf error msg was solved by:sudo aptitude install gtk2-engines-pixbuf But still gksu or gksudo aptitude (and others like synaptic and others as well, i'd suspect ...) do not work.
I searched for:Unable to locate theme engine in module_pathand came up with some interesting results ...one idea that stick out means reinstalling the theme you are using:sudo apt-get install --reinstall gtk2-engines
sudo apt-get install gtk2-engines-pixbuf
sudo apt-get install --reinstall gtk2-engines gtk-murrine-engine gtk-equinox-engineor what ever ...
I have the mozjpeg-git package so there's no libjpeg-turbo or similar stuff indeed, so when upgrading gdk-pixbuf2 this isn't surprising:g_module_open() failed for /usr/lib/gdk-pixbuf-2.0/2.10.0/loaders/libpixbufloader-jasper.so: libjpeg.so.8: cannot open shared object file: No such file or directory
g_module_open() failed for /usr/lib/gdk-pixbuf-2.0/2.10.0/loaders/libpixbufloader-jpeg.so