Optimization of keying clip operations

Gives around 20%-30% speedup by doing early exit from
kernel traversal cycle.
Fix T40320: wrong render layer visibility with cycles deformation motion blur.
Fix crash rendering linked scenes in compo

Simply linking scene (lib.blend) without compo into another one (compo.blend),
using it in a compositor and rendering it would crash.
Some operation allowed to set invalid active scene render layer

Forbid this now and do tricks in the versioning code to repair
corrupted files.

Thanks to Pablo, Caminandes and Koro for discovering this bug!
Cleanup: Comments and unused variables.
msvc 2008 platofrm suffix changed to be -vc9
Fix T40331: Incorrect display of path of editted data.
Revert "Cycles-Bake: fix T40322 Glitch in baking a mixed SSS shader"

This reverts commit 81b129d3b837e31c0d6d2a9d2a6e39d39e47c1ec.

This is not the correct fix yet. More details in T40322
Fix T40438: Pressing G key to move the camera quits Blender.
Freestyle: Partial fix for thinning strokes due to flipping stroke directions at TVertices.

A description of the problem is found in https://developer.blender.org/T36425#19 .

The cause of the issue was identified as roudning errors in Operators::createStroke() due
to insufficient numerical precision.  Precision promotion from float to double was done in
the return values of getPoint3D/2D methods in Interface0D and its subclasses in C++
(data members stored in the 0D classes have already been in double precision).
Fix Sequencer OpenGL render ignoring preview channel
Fix for curve having invalid active vertex after setting type

also allow passing NULL vertex to BKE_curve_nurb_vert_active_set
EditCurve: Replace -1 with CU_ACT_NONE define
Fix curve switch direction ignoring active vertex
Fix for BLI_delete failing on files containing quotes
Fix for thinning strokes at intersections between visible and background hidden lines.

This commit is intended to fully fix the problem described in
https://developer.blender.org/T36425#19 (see also the previous commit rB08528f577dcb).

Addition of a small offset (to avoid singularity in stroke rendering due to overlapping vertices)
was not performed for all overlapping vertices.

Removed the StrokeCleaner and related helper functions which were added as a
temporary workaround in rB2a5b6d9c8f16.
Workaround T40317: Ghost/Win32 keys sticking for new windows

Ghost win32 ignores key-up events for newly activated windows.
for now just disable code for win32 to initialize modifiers for new windows.
Fix for a missing code update in my commit rB08528f577dcb.
Fix T40359: Scene / Color Management: White Point Mapping Has Limit
Fix T40354: Camera Tracks in the Dope Sheet can't be deselected