Revert "Fix T53850: Lock to Cursor breaks 3D manipulators"

This reverts commit f93a6857d8dc15d4be81feafd6dad6ef04d0bd31.

Was intended for 'blender-v2.79a-release' branch.

Fix T53850: Lock to Cursor breaks 3D manipulators

Docs: update API changelog to 2.79

Update submodules to 2.79 release commits.

Should have been done before ahoy, sorry about that. Means 2.79 tag will
be one (no functionnal changes) commit ahead from our 2.79 builds, think
we can live with that.

Update release cycle to 'release'.

Fix T52696: Sculpt - Brush spacing pressure artifacts

Was caused by divide-by-zero in paint_stroke_integrate_overlap()
in paint_stroke.c, as identified by Bob Smith (uvwxyz).

Thanks for the report!

Fix T52701: Mesh shortest path fails at boundaries

PyAPI: Fix mathutils freeze allowing owned data

Fix T52531: Blender 2D stabilisation node issue when autoscale is selected

Threading conflict, should be safe for 2.79.

Cycles: Safer fix for infinite recursion

Previous fix wasn't working correct for certain compiler and CPU intrinsics
mode, causing quite some crashes.

This should be a safer fix, which is closer in behavior to previous release
but which should still fix issues with robust curve intersection.

Fix T52650:Grease pencil selection its not automatically updating in Clip Editor

Math Lib: normalized vector project functions

Fix T52149: LoopTriArray computation was not correctly protected against concurrency.

Note: this commit seems to work as expected (also with transform
snapping etc.). However, it is rather unsafe - not enough for 2.79 at
least, unless we get much more testing on it. It also depends on three
previous ones.

Note that using a global lock here is far from ideal, we should rather
have a lock per DM, but that will do for now, whole DM thing is doomed
to oblivion anyway in 2.8.

Also, we may need a `DM_DIRTY_LOOPTRIS` dirty flag at some point. Looks
like we can survive without it for now though... Probably because cached
looptris are never copied accross DM's?

Cleanup: remove useless `DM_ensure_looptri()`.

That one was doing exactly same thing as `dm->getLoopTriArray()`, no
point in having twice the same code here...

Fix transform snap code using 'allocated' flags to get verts/edges/etc. arrays again from DM.

This was... horribly wrong, CDDM will often *not* need to allocate
anything to return arrays of mesh items! Just check whether array
pointer is NULL.

Also, remove `DM_get_looptri_array`, that one is useless currently,
`dm->getLoopTriArray` will always return cached array (computing it if
needed).

Cleanup: deduplicate DM's getLoopTriArray() callback.

All three functions were doing exactly the same thing, simpler to only
have one in that case!

Fix T52639: Weight paint smooth tool crash

UI: fix memory leak when copy-to-selected failed

Fix T52678: Crash editing gpencil w/ frame-lock

Screw Modifier: remove doubles option

Vertices on the axis can be optionally merged,
nice for creating objects which close at the end-points.