Warn that ++ is not atomic (on longs?)

From email:

Here's another warning the compiler could give. For the
second time in a week, I've seen code like:

     public Random() { this(++seedUniquifier ....); }
     private static volatile long seedUniquifier = 8682522807148012L;

where it looks like people think that declaring seedUniquifier
to be volatile means that ++seedUniquifier will work like an
atomic operation. I know it doesn't, and you know it doesn't,
but "people" seem to think it does, hence the need for the
warning. You might get a lot of false positives, though, like
this one in java.util.Random, where the ++ doesn't *have* to
be atomic.