This functionality was present until Blender 2.80. Basically it adds back the
"+" and "-" buttons in the file browser when it stores an output filepath.
This is useful for someone rendering multiple versions of an animation (or a
composition) to compare.
At the moment this is used for the render output, and the File Output node in
the compositor.
Differential Revision: https://developer.blender.org/D15968
78bfaf1a4f