This fixes#61, and addresses one item of #14.
* src/ltlvisit/relabel.hh: Use a map rather than a unordered_map,
because the Swig binding for unordered_map do not seem functional.
* wrap/python/spot_impl.i: Adjust.
* wrap/python/tests/relabel.py: New file.
* wrap/python/tests/Makefile.am: Add it.
* doc/org/tut02.org: New file.
* doc/Makefile.am: Add it.
