and URANDOM_DEV used for seeding.
Fall-through seeding if there are problems opening URANDOM_DEV.
Use random() and srandom() where available as it's considered quite a bit
better than rand().
Define (but don't use) HAS_SRANDOMDEV_FUNC to indicate that srandomdev()
is avaiable.  The reason it's not used is that xp_randomize() returns the
seed value presumably to make it possible to replay a random sequence and
srandomdev() creates states which cannot be replicated on demand.