Blender Git Loki

Fix [#21756] Texture paint "quick edit" sending wrong path on unsaved scenes

* Made it use the temp directory in user preferences when the .blend file hasn't been saved yet
* Made bmain->name (wrapped as bpy.data.filename) contain an empty string when
there's no .B25.blend and no file saved, rather than "<memory2>".

This is a good candidate for consistent file path api, retrieving temp dirs / project-
specific temp dirs / etc...