Clean up bogosities in use of random(3) and srandom(3) --- do not assume

Clean up bogosities in use of random(3) and srandom(3) --- do not assume
that RAND_MAX applies to them, since it doesn't.  Instead add a
config.h parameter MAX_RANDOM_VALUE.  This is currently set at 2^31-1
but could be auto-configured if that ever proves necessary.  Also fix
some outright bugs like calling srand() where srandom() is appropriate.