Blender Git Loki

Cycles ctests: Run blender without system script override

The idea is to force using Cycles tests only after running install target.
More i'm thinking about ways to not require this more it's clear there is
no clear way to support this. It is possible to hack something around and
make tests to be running smoothly, but it's never gonna to give all the
features (like GPU which required source file on linux and compiled cubin
on windows, OSL which requires compiled script) without any manual tweaks
anyway.

So let's be damn stupid and not try to be smart and just assume install
target was run which makes Cycles tests just happy without any extra
setup. Would be nice to detect and report missing target install so we
don't spend time on rendering Cycles scenes with Blender Internal.