Revision 140834

* DoubleArray is now an interface which is implemented by
ExpandableDoubleArray.  The interface provides a public interface
which does not hint at any of the storage parameters of
Expandable or Contractable.

* DoubleArrayTest now operates on the DoubleArray interface, casting
to Expandable when we need to call the package scopes getInternalLength
method.

* While we should not provide access to the internal storage array, it
should be possible to obtain a double[] of elements stored in this
DoubleArray - double[] getElements() was added to the DoubleArray interface,
it will return the element array.