Merged changes in the trunk up to revision 53584.

Conflicts resolved:
release/scripts/startup/bl_ui/properties_render.py
source/blender/blenloader/intern/readfile.c
source/blender/editors/interface/interface_templates.c
source/blender/makesrna/RNA_enum_types.h

Also made additional code updates for:
r53355 UIList - Python-extendable list of UI items
r53460 Alpha premul pipeline cleanup

release/scripts/startup/bl_operators/__init__.py

@@ -47,7 +47,7 @@ _modules = [
 
 import bpy
 
-if 'FREESTYLE' in bpy.app.build_options:
+if bpy.app.build_options.freestyle:
     _modules.append("freestyle")
 __import__(name=__name__, fromlist=_modules)
 _namespace = globals()