Blender Git Loki

Use gnu89 for GCC

GCC5 defaults to gnu11, which we may switch to later
but disable for now to prevent accidental use.

BLI_utildefines: add MEMSET_STRUCT_OFS macro

Fix T44530 UV islands fail on subsurf after mirror modifier.

Caused by own commit that changed island detection code. In the case of
modifiers we don't want to take winding information into account, but
left the code since there are use cases (like painting) which could use
this.

Project Paint: Add symmetry support

- Access from symmetry panel (as with sculpt)
- Supports multiple axis at once.
- Supports all brush types including clone.

Fix T44516 grid lines obscuring selection outline.

Was changed to draw after meshes without depth mask to make grid not
contribute to compositing effects. Now only draw it like this when we do
compositing (unfortunately can't have both).

Fix for Clang type check

Added missing update tag to recalculate data after permutating materials

adding sample python template for ui preview icons

Hide app and BPyPreviews classes from utils namespace.

__all__ is rather useless in the end... Chose a bit of a convoluted way to do it,
maybe using hidden '_'-prefixed names would be better/simpler?

Minor tweak.

Merge branch 'master' into ui-preview-buttons

fixing problem with deleting a previews collection

Merge branch 'master' into ui-preview-buttons

Add 'readonly dict-like' behavior to high-level previews collection.

And some cleanup/rename/documentation/...

Rework previews handling to be 'simpler' on py-level, as discussed with Campbell

This removes ID-free previews handling from RNA, adds a low-level hidden API
in bpy.app._previews, and the real previews manager in bpy.utils.

There is still lots of cleanup and renaming to be done...

Merge branch 'master' into ui-preview-buttons

Merge branch 'master' into ui-preview-buttons

Merge branch 'master' into ui-preview-buttons

Fix broken uiTemplateIconView().

Was using enum **value** as **icon id**... tripple sigh!
Guess it was working for its only current use (matcaps), but still.

Merge branch 'master' into ui-preview-buttons