[daip] random number generator in IMMOD (and likely others)

[Eric Greisen]

It is not a good random number generator and depends on a kernel to
start it.  If you run it twice in the same second you will get
identical results.  I really should fix this somehow.  Computers are
faster now so one could do more initializing.  But the real-time clock
is still in integer seconds.

I will modify the initializer so that when you are a few seconds apart
you get quite different numbers.

Eric Greisen