Code Cleanup: remove object arg to CDDM_from_mesh mesh_create_derived
BGE: Add missing NULL check from recent LOD updates
correction to last commit
Fix T37939: Crash on exit (reading from freed node trees)
Correct alloc string and comment in makesdna
correction to last commit
Cycles / Hair: Some cleanup and optimizations for hair code.

* Remove dead code from line segments BVH refine.
CURVE_KN_TANGENTGNORMAL and CURVE_KN_TRUETANGENTGNORMAL are either both true, or both false. Therefore a true/false condition is impossible.
This was a leftover of CURVE_CUSTOM, which was removed in r59234.

* Use "else if" in blender_curves.cpp.
Fix T37946: Error filling ngons
Polyfill: minor changes to which fix rare errors with float precision
Cycles / Hair: Further cleanup of UI and internals.

* UI: Remove deprecated condition (CURVE_RIBBONS) and hide backface property, when it's hardcoded in C (Curve/Line segments && Ribbons).

* Remove "use_tangent_normal" and "CURVE_KN_TANGENTGNORMAL" as its unused (follow up for last commit).
Simplify isect_point_poly_v2 functions using angle_signed_v2v2
Fix T37945: Crash after undo

Issue was caused by some typos in readfile.c made in
original commit of image cache rewrite.
Threaded object update and EvaluationContext

Summary:
Made objects update happening from multiple threads. It is a task-based
scheduling system which uses current dependency graph for spawning new
tasks. This means threading happens on object level, but the system is
flexible enough for higher granularity.

Technical details:

- Uses task scheduler which was recently committed to trunk
  (that one which Brecht ported from Cycles).

- Added two utility functions to dependency graph:
  * DAG_threaded_update_begin, which is called to  initialize threaded
    objects update. It will also schedule root DAG node to the queue,
    hence starting evaluation process.

    Initialization will calculate how much parents are to be evaluation
    before current DAG node can be scheduled. This value is used by task
    threads for faster detecting which nodes might be scheduled.

  * DAG_threaded_update_handle_node_updated which is  called from task
    thread function when node was fully handled.

	This function decreases num_pending_parents of node children and
	schedules children with zero valency.

    As it might have become clear, task thread receives DAG nodes and
    decides which callback to call for it.

    Currently only BKE_object_handle_update is called for object nodes.

    In the future it'll call node->callback() from Ali's new DAG.

- This required adding some workarounds to the render pipeline.
  Mainly to stop using get_object_dm() from modifiers' apply callback.
  Such a call was only a workaround for dependency graph glitch when
  rendering scene with, say, boolean modifiers before displaying
  this scene.

  Such change moves workaround from one place to another, so overall
  hackentropy remains the same.

- Added paradigm of EvaluaitonContext. Currently it's more like just a
  more reliable replacement for G.is_rendering which fails in some
  circumstances.

  Future idea of this context is to also store all the local data needed
  for objects evaluation such as local time, Copy-on-Write data and so.

  There're two types of EvaluationContext:

  * Context used for viewport updated and owned by Main. In the future
    this context might be easily moved to Window or Screen to allo
    per-window/per-screen local time.

  * Context used by render engines to evaluate objects for render purposes.
    Render engine is an owner of this context.

  This context is passed to all object update routines.

Reviewers: brecht, campbellbarton

Reviewed By: brecht

CC: lukastoenne

Differential Revision: https://developer.blender.org/D94
Bullet: Update to svn r2719

Fixes part of T37905, fixed constraint didn't work correctly.
Avoid temporary change of animation data flags for nodes filter

Use temporary runtime flag of filter_mode argument instead.

This commit also fixes some weirdo mix of filter_mode with
filterflag bits.
Usual minor UI messages fixes...
Rigidbody: Add option to choose mesh source for collision shapes

The options are:
Base: Base mesh
Deform: shape keys and deform modifiers
Final: All deformations and modifiers

It would be nice to have a way of specifying where exactly in the
modifier stack the collision shape is generated. However this is not
staight forward since the rigid body simulation is not part of the
modifier system and would require hacks to make it work.
Rigidbody: Use own structure to store mesh data for collision shapes

This gives us better access to the data and should also be faster to
create.
Rigidbody: Allow triangle mesh shapes to deform during simulation

Only supported when using the "Deform" mesh source.
Fix out-of-date comment which came from DAG-MT branch