Fix#505, Reported by Edmond Irani Liu.
* spot/twa/twagraph.cc (copy): Deal with kripke_graph in a better way.
* spot/twaalgos/hoa.cc: Do not force the use of named-states since
when the input is a kripke_graph.
* tests/python/kripke.py: Adjust test cases.
* NEWS: Mention the change.
* THANKS: Add Edmund.
Related to issue #376.
* spot/kripke/kripkegraph.hh: Avoid indirect type definitions for the
benefit of Swig.
* python/spot/impl.i: Add bindings for iterators over kripke_graph
states and edges.
* tests/python/kripke.py: New file.
* tests/Makefile.am: Add it.
* NEWS: Update.