Remove the horror that was the global smb_rw_error.

Remove the horror that was the global smb_rw_error.
Each cli struct has it's own local copy of this variable,
so use that in client code. In the smbd server, add one
static to smbd/proccess.c and use that inside smbd. Fix
a bunch of places where smb_rw_error could be set by
calling read_data() in places where we weren't reading
from the SMB client socket (ie. winbindd).
Jeremy.
(This used to be commit 255c2adf7b6ef30932b5bb9f142ccef4a5d3d0db)