4.3BSD UWISC "newfs: ra81: no default block size for `c' partition" fix

When partitioning slice c of an RA81 disk under 4.3UWISC, you will get the following error:

newfs: ra81: no default block size for `c' partition

Despite /etc/disktab appearing complete, this error is unavoidable. In order to properly partition an RA81 run the following command:

/etc/mkfs /dev/rra0c 891072 51 14 4096 512 16 10 60 2048 t
#         special    size [ nsect ntrak bsize fsize cpg minfree rps nbpi ]

This can be retrieved using newfs -v special when newfs fails in this way.

It is likely this could also be used to circumvent whatever issue is causing the write error: 759667 error when installing to an RA81.