ThreadLocalRandom clinit troubles

[Martin Buchholz]

Thanks to Peter for digging into the secure seed generator classes and
coming up with a patch.  Openjdk security folks, please review.  I confess
to getting lost whenever I try to orient myself in the twisty maze of seed
generator implementation files.

Anyways, it seems important to have prngs like ThreadLocalRandom be able to
get a few bits of seed entropy without loading hundreds of classes and
without occupying any file descriptors permanently.  Perhaps at Google we
will go back to writing some simple non-portable startup code to read
/dev/urandom until openjdk security team comes up with a more principled
solution (but one that doesn't drag in too much machinery).