Initialising random(4)

This program initialises the pools in random(4) with data from
/dev/urandom on the machine that does the compile. The output is
different every time it runs. This is not necessary in many cases, but
it is cheap, can do no harm, & may block some attacks.

Eventually I'll get around to submitting patches -- add this program
and do some minor fiddling with random.c and the makefile -- but quite
likely not soon, so here's the code in the meanwhile. Comment
solicited.