For those want to testdrive the navigation (Joy-right/Select) and launch game (Start) also for the image slideshow screen saver -see suggestion 4 above- are invited to do so:
git clone https://github.com/RetroPie/EmulationStation.git
cd EmulationStation
git fetch origin pull/673/head:slideshow-controls
git checkout slideshow-controls
cmake -DFREETYPE_INCLUDE_DIRS=/usr/include/freetype2/ -DGL=On -DRPI=On . && make -j 5 all
./emulationstation --debug