This uses the same trick as discussed in issue #566 and issue #568.
* spot/twaalgos/determinize.cc (safra_support): Use a basis
if it is smaller than 2^|support| for the current Safra state.
* tests/core/568.test: Add some tests.
* NEWS: Mention the optimization.
Closes issue #568.
* spot/twaalgos/simulation.cc (direct_simulation::build_result):
Implement an alternate loop based on edge_separator::basis to iterate
over a signature to build results.
* tests/core/568.test: New file.
* tests/Makefile.am: Add it.
* NEWS: Mention the optimization.