The bug is mentioned by Maximilien Colange in a comment to issue #317,
but turned out to be unrelated to that original issue.

* spot/twaalgos/totgba.cc (dnf_to_streett): Save the correspondence
between the created states an the DNF clause in a named property.
* doc/org/concepts.org, spot/twaalgos/totgba.hh: Mention the new
property.
* spot/twaalgos/cobuchi.cc (save_inf_nca_st): Rewrite using the named
property.  Relying on seen marks and trying to deduce the matching
original clause could only work from plain Rabin.
* tests/core/dca.test: Add the test from Maximilien.
* NEWS: Mention the issue.