I am guilty of an act of ommission. There is no longer a /dev/urandom

I am guilty of an act of ommission. There is no longer a /dev/urandom
device with Yarrow, and although I coded for that in dev/MAKEDEV, I forgot
to _tell_ folks.

This commit adds back the /dev/urandom device (as a duplicate) of /dev/random,
until such time as it can be properly announced.

This will help the openssl users quite a lot.