When a GEOM (/dev-)device is closed and we find that I/O requests are still outstanding, give them a chance to complete.
When a GEOM (/dev-)device is closed and we find that I/O requests are
still outstanding, give them a chance to complete.

If after 10 seconds we still find outstanding I/O requests, complete
the close with a console warning that the system is likely to panic
later on.

This is a workaround for umount -f not quite doing the right thing.

Approved by:    re/scottl

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase