bikeshedding: sizediff_t -> size_s ?

[Andrej Mitrovic]

I've noticed this thread a while ago:
http://thread.gmane.org/gmane.comp.lang.d.phobos/3881/focus=3885

Maybe it's way too late for any changes, but I think sizediff_t is a
mouthful. Doesn't size_s look nicer? It would be size_t's evil twin
brother, look:

size_s  imSoNegative;
size_t  neverADowner;