Good points, Jeffrey.  Documentation can be improved and cond.wait_for(pred) is indeed not guaranteed to wake up when predicate is true unless someone calls notifyAll.

I spent some time thinking of a name.  I tried wait_predicate and predicate_wait, but wait_for seemed natural.  Any other ideas?
How about wait_until_true?

My original method had this as a free function, but I moved it into the Condition because I could see no other kind of primitive that would use it.  I agree that it is unfortunate to pull what is essentially a utility function into the Condition variable, so I am leaning towards keeping it a module function.