Cycles Network rendering, remove some exception throwing, replace with saner error handling

This patch adds a network_error() function more alike how other devices handle error's

- it adds a check for errors on load_kernels to make sure we do not crash if rendering without a server.
- it uses the non throwing variation of boost::asio::read.

Reviewers: brecht

Reviewed By: brecht

CC: brecht

Differential Revision: https://developer.blender.org/D86
Fix lamps drawing only partially in OpenGL render.

It should draw lamps entirely, this happened due to hack to hide object centers.
Fix T38500: Audio of a scene strip can't be muted

Exposed Audio Volume of a scene to properties of a scene strip.
Fix T38498: properly unlink scene pointers from SpaceNode.

This fixes the first case mentioned in the report. Has to do some ugly
DNA access to SpaceNode, unless we'd allow a bad level call there to do
it in ED_node ...

The second case has been fixed by @sergey in D274:
https://developer.blender.org/D274?vs=838&id=879#toc

So actually asan just did its job here, good to know!
Remove unnecessary debug print
Fix wrong animation duration when using older Libav
Bye-bye FAST!

FAST detector has been replaced with fancier Harris,
so no need to keep FAST library in the sources now.
Cycles: add pass alpha threshold value to render layers.

Z, Index, normal, UV and vector passes are only affected by surfaces with alpha
transparency equal to or higher than this threshold. With value 0.0 the first
surface hit will always write to these passes, regardless of transparency. With
higher values surfaces that are mostly transparent can be skipped until an opaque
surface is encountered.
Fix compile error in last commit, forgot to include this change.
Fix T38515: python menu tooltip description affecting unrelated menus.
Fix T38516: crash when using color picker from redo panel.
Patch T31269: Add sewing seams to cloth simulation

Description:
--------------------------
Use loose edges marked as seams as sewing springs.

Usage:
-------------------------
All this patch does is set the rest length to 0 and the stiffness to 1 for springs for loose edges marked as seams so that during the cloth simulation they will be brought together.

Example Video:
-------------------------
http://www.youtube.com/watch?v=-Y_bC0gjoM0

Original Patch by thesleepless (+ git patch by codemanx)

Thank you!
Fix T38524: Cycles not rendering sky texture correct when the direction vector is not normalized.
Fix T38526: crash using blackbody node on background with multiple importance sampling.
UI: Fix Cloth panel after 28936a415076, was too large and looked bad.

* Move Sewing Springs to a dedicated panel, the "Cloth" panel is too crowded already, and the sewing springs feature is nicely isolated.
* Typo fix.
Quiet warning
Fix T38503: crash in non-threadsafe VBO free code during render.
Fix T38521: skin modifier crash with zero radius vertices.
Fix T36979: wrong render of textured mesh lights with multiple importance sampling.