Bury ordering structures and their alloc+free inside order.c

Bury ordering structures and their alloc+free inside order.c
- nothing outside order.c needs this stuff, TSI alloc+free routines
  have no business being exported
- for now we need to store a pointer to tsortInfo in the elements,
  its just an opaque pointer for ping-ponging the data through ts elements
- all allocation + freeing is local to ordering code