Remove busy wait from AtomicSafeInitializer.get()

Placeholder ticket for https://github.com/apache/commons-lang/pull/46

Remove the busy wait from AtomicSafeInitializer.get().

Also ensure waiting threads do not wait indefinitely after initialize() throws an exception, instead throwing the same exception, re-wrapped, for each requester.

Brought the unit tests up to 100% coverage on AtomicSafeInitializer. Eliminated race condition on verifying at least one thread waiting for initialize() to complete in another thread.