Blender Git Loki

RNA comparison/override: better control over property processing.

This commit essentially introduces a new RNA property flag, which when
set prevents affected property from being processed at all in comparison
code (also used to automatically generate static override rules).

The idea is to use it on very low-level data in RNA, like e.g. mesh's
geometry or psys' particles collections.

For now only applied to psys' particle collections, on the main mesh of
Agent327 pigeon, it goes from 100ms to 0.5ms on a full
auto-override-generating comparison...

Also added some new RNA property helper funcs to check on comparable and
overridable status.