[Cin] fileexr/fileppm direct copy support

[Andrea paz]

> try to render first exr sequence (from any source) . Set EXR compression to some cpu intensive choice.
> Then load this sequence and in rendering dialog only change name of sequence, so it will create new set of images.
> Try last step with patched and unpatched cingg.

These are exactly the steps I took. I used "none" or "RLE" compression
with the same results. I also tried rendering a tiff sequence still
with the same results (21 fps).

> RAM flushed to relatively slow disk?

I have 32 GB of RAM and nvme disk. No more than 3 GB is ever used
during rendering and swap is not used.
Today I no longer have the 80% slowdown! I wonder what had happened to
my PC yesterday?