some cleanups from the conversion of Pipes[] to a linked list. I also

some cleanups from the conversion of Pipes[] to a linked list. I also
removed most cases where a pnum is used and substituted a pipes_struct*.

in files.c I added a offset of 0x1000 to all file handles on the
wire. This makes it much less likely that bad parsing will give us the
wrong field.
(This used to be commit 8bc2627ff28d340db65bfa017daca2dc291d5ef7)