Expand out the swap_read()/swap_write() functions inline, since they were only called...

Expand out the swap_read()/swap_write() functions inline, since they were only called once, and they were supposed to be abstract but now the abstract part is done by core_to_swap_copy()/swap_to_core_copy() and the rest is well defined -- makes core.h/swap.h and core.c/swap.c identical again except for core<->swap