This is motivated by an example sent by Edmond Irani Liu,
that will be tested in next patch.

* spot/twaalgos/dbranch.cc, spot/twaalgos/dbranch.hh: New files.
* python/spot/impl.i, spot/twaalgos/Makefile.am: Add them.
* spot/twaalgos/translate.cc: Call delay_branching_here
unconditionally.
* spot/twa/twagraph.cc (defrag_states): Do not assume
that games are alternating.
* tests/core/genltl.test: Adjust expected numbers.
* tests/python/dbranch.py: New file.
* tests/Makefile.am: Add it.