8237514: Spec Clarification - ByteBuffer::alignmentOffset Spec

[Brian Burkhalter]

This patch [1] is proposed for [2] which follows from the fix for [3] concerning the ByteBufffer.alignmentOffset() specification. In particular this adds a precondition, value <= index, on the first identity and attempts to improve the verbiage of the specification in general. Some code is added to the test to verify the identities.

Thanks,

Brian

[1] http://cr.openjdk.java.net/~bpb/8237514/webrev.00/
[2] https://bugs.openjdk.java.net/browse/JDK-8237514
[3] https://bugs.openjdk.java.net/browse/JDK-8230665