function calls. Broken tracking of open partitions gets fixed as a side
effect. Races in sdopen() and sdioctl() become more numerous than before.
Close the device in sdsize(). Media removal could not have worked right
when unused swap devices were held open. There may now be a problem
with used swap devices not being held open.
Fix ancient operator precedence bug in sddump(). It may have been
possible to attempt dumping to unloaded media.
Remove NetBSD ifdefs. We're too different now, and the NetBSD driver was
already too different for them to be relevant.
Remove support for soft write protection. There are no ioctls to set it,
and this driver never set it either. It was used in the wd driver to
disable writing to unlabelled disk, but we want to support writing to
foreign partitions on unlabeled disks.
Clean up some formatting and restore some old-style function headers.