Fix crashing regression in Armature EditBone Select shortest path/Select Linked actions.

Dummy typo in some recent refactor I guess.

This is to be backported to 2.72 for sure!
Fix T41977: 'Shading' panel of Render buttons not updating Rendered 3DView.

Reuse `rna_Scene_glsl_update` here too.
Fix T41993: Constant jittered bug

Rotated coordinate of the ray start was used when calculating
the ray direction, ending up with wrong direction.
Fix T41905: Linked objects/groups assigned to 'wrong' active layers when called from 3DView

Typo using v3d->layact instead of v3d->lay when linking and v3d is available in context.

This can be backported to 2.72.
Revert previous commit (sorry about that), and use standard func to get active layer
in this case too.

Thanks to Campbell for the head up.
Fix T41988: Shadow pass inaccurate calculation
Update for release themes.

This is to be backported to 2.72.
Cleanup: style
Fix BI viewport render crash happening with zero render border area

This is better to be backported to the 2.72.
Libmv: Update Ceres to the latest upstream version

Mainly to let ITERATIVE_SCHUR use an explicit Schur Complement matrix.
Libmv: Enable explicit Schur complement matrix by default

Gives up to 2x speed up of camera solving process in average scene.
In the really huge one it might be slower, but that we need to investigate.
Blend modes: fix array length being too short

Reviewers: psy-fi

Differential Revision: https://developer.blender.org/D799
Libmv: update ceres to latest upstream version

This brings faster BlockRandomAccessSparseMatrix::SymmetricRightMultiply.
Use native float math functions for MSVC12

`double` surrogates are slow (e.g. pow is 2x slower than powf), and MSVC12
supports fp-math functions from C99.
Fix T42018: Crash when displaying beveled poly-curves with spline bevfac mapping

This fix is for 2.72.
fix T42022 Attempt to export empty set of objects resulted in an exception
Style cleanup
Fix compilation on GCC (good old mixed declaration and code).
Fix T42026: Unit scale affects camera focal length.

Not a regression, yet maybe simple/safe enough for 2.72?
Support for "virtual pixelsize" on 4k screens.

On 4k devices the default pixel size leads to tiny OpenGL drawing
that is hardly usable without doubling the DPI. The retina system
on OSX aims to alleviate this problem by introducing a general 2x
pixel size.

No equivalent feature exists on other platforms so far. However,
to emulate the effect this patch introduces a "virtual" pixel size
factor for OpenGL drawing.

Note that the user currently has to enable this manually by selecting
the "Virtual Pixel Mode" in the user preferences (defaults to native).
All windows of a Blender instance share the same virtual pixel size as well.
It may be possible to handle this on a per-window basis and automate
the selection somewhat (if enabled by the user), so working with
multiple screens becomes more convenient, but technical limitations
make this a bit difficult (on X11 with nvidia drivers the actual screen size
is not reported correctly).

Reviewers: ton, campbellbarton

Differential Revision: https://developer.blender.org/D669