start.sh: be clever about $SESSION_MANAGER

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Ignore more files

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
fixup! Work around missing avcodec_free_frame
Applied patches/old-libav.patch

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>