support for cycles/sharing, a bug fix, and other changes (see below):

- cycles and sharing detected through System's hashcode identity, though
external value copies will lose sharing when serialised. Cycles blow up
JAXB serialisation
- revised Dynamic APIs to avoid implicitly casts: wrappers are and
should not be visible, copies should be immediately serisalised.
- fixed bug on external value copies of empty lists and maps, wrappers
now pre-initialised.
- full Javadoc documentation on Dynamic