In perl versions up to 5.003 (I think), srand needed to be
called explicitly, but as of 5.004 (again, I think), srand
was called implicitly with the first call to rand. Wnen
srand is called implicitly however, the seed it is given is
a number based on the time, which is predictable, so it's
recommended to call it again with a better seed if it's for
something more important, like cryptography purposes.