Further tweaks to SCons's auto tests

We should do autotests only after setting path to sconsign,
otherwise using the same working directory and different
build directories will eventually break.
Cleanup: Always assign num_samples, there is no need for this special define.
Cleanup: Same thing in path trace setup, we can safely always assign the proper value.
Fix T40909: BGE softbodies broken.

Looks like softbody settings got lost in a recent cleanup.
SCons: Hopefully final fix for 32bit linux buildbot

No need to run automated tests for cudakernels target. TThis could
be harmless because CUDA binaries are built in the another chroot.
Need to disable Libmv for cudakernels target

This way no access to automated tests variables will happen.

Ideally it should be something more like using blenderlite
with just Cycles enabled, but let's keep it for a bigger
clean up.
Revert "Fix T40257: Frustum culling not working properly"

This reverts commit 978dba4616852e0b94374f2ae56934049d9b3669. The change
still doesn't provide accurate culling information, and actually breaks
animation culling.
Fix compilation error with scons when building from detached head
Fix for invalid memory access in graph editor when deleting the last
vertex in a fcurve.
Fix T41005: Seemingly random crashes with cycles rendering
Fix T41013: OSL and Crash
Fix T40989: Intermittent crash clicking material color selector

Issue was caused by not enough precision for inversion threshold.
Use double precision for this threshold now. We might want to
investigate this code a bit more further, stock implementation
uses doubles for all computation. Using floats might be a reason
of bad rows distribution in theory.
Cycles: Add link to a paper used for Beckmann table calculation

This is for those who'll be reading code and trying to improve it.
WIP
test-not-finished