Libc memcpy/etc. fixes

Includes #309.  I don't know of any games this fixes so may be better to defer until later.  That said, the return value for memcpy/memset was definitely wrong.

Probably makes `sceKernelMemcpy()` slower, but trying to be more accurate in case it matters.  I don't see it called often so I'm not too worried about speed, but I'm happy to revert that change.

Makes  hrydgard/pspautotests#35 pass.

-[Unknown]