So, as part of the ongoing saga of improving the tty interface, I'm
about to make the following change:

Add a new field to struct tty -- ts_wopen.  This will be used
whereever the TS_WOPEN bit is currently used, but will instead keep a
*count* of the processes waiting to open the device.  This can be used
when an open fails to determine whether any other processes are
waiting, and thus whether the device should be shut down.  (Currently
there is no way to do this without device-specific hacks, which
defeats the point of having TS_WOPEN in the first place.  In fact, we
mostly get this wrong.)

Although it would be easy to be backward-compatible here, on the
general theory that cruft tends to never go away, I will *not* do so.
This will simply make drivers that haven't been updated fail to
compile, which isn't particularly harmful.