[Cin] Rendering multi-threads

[Andrea paz]

Render farm is OK, now. Thanks.

I did some more rendering tests:
CPU 8c/16t
"use HW device" --> none
Container: mp4
codec: h264

Default (none or threads=0) --> 86.5 fps

[note: does not vary by changing SMP (obviously); I tried SMP=4; 8 and
14 with the exact same result]


threads=8 --> 64.2 fps

threads=15 --> 72.8 fps (I read somewhere that ffmpeg handles up to 15
threads; I don't know if this is true)

threads=16 --> 73.2 fps

[Note: in all these tests, from Top you can see that the rendering
starts from 1000 - 1200%, but then after about ten seconds, it goes to
400 - 600% until the end of the rendering.]

Render farm OK: all the cores at 100% --> 170 fps


When I compile CinGG, I use this "configure":

env CUDA_PATH=/opt/cuda ./configure --without-oss  --with-cuda
--with-single-user --with-booby

maybe I need to add/take out some flags? (e.g. --prefix=/usr)