[Cin] Cingg bg render crash video scenario

[Andrea paz]

In my opinion, one possible source of BR problems is when we use CinGG
as normal users, but the default BR folder is in /tmp and thus
requires root privileges. Perhaps it would be better if CinGG created
a default folder in .../cinelerra5/cinelerra-5.1/.
My other request: is it possible to create a button that deletes all
BG image files from inside CinGG? Maybe near the input window for the
path of such files. In fact, I believe that even the permanence of
files of one format are problematic when you want to change formats.
This is not an important request because when you use a format you
continue to use that format; however, it can prevent possible crashes.