* Not strictly necessary right now, but better for future.
* Struct data (only boids at the moment) is now written as structs (with dna) so they work between 64 and 32 bit machines too.
Particle cache reading: crash when loading .blend on a different
endian system, code was dumping arrays in .blend without DNA.
General warning for devs: avoid generic write_data and dynamic
arrays in DNA.