Blender Git Loki

Particles: Interpolate size for interpolated children

This finally allows us to use Random factor to add variations to the
interpolated children. This feature never worked since 2007L there was
random factor slider in the interface, but it was only used by simple
children. Now it has affect on interpolated children as well.

Technically, this will break compatibility if older file had random
factor set to something else than 0 (default value is 0 though). But
we are leaving 2.7 series, so can accept such breackage in the name
of supported features.