Operator &= used to always move Fin to the front, it does not anymore.
The only thing it does now is to merge Inf(x)&Inf(y) as Inf({x,y}).
Operator |= is now symmetrical and merges Fin()s.
Fixes#253.
* spot/twa/acc.cc, spot/twa/acc.hh: Simplify &= and make |= symmetrical.
* spot/twaalgos/cleanacc.cc: Fix conjunction order.
* tests/core/acc.test, tests/core/acc2.test, tests/core/parseaut.test,
tests/core/readsave.test, tests/core/satmin2.test,
tests/core/sccdot.test, tests/python/acc_cond.ipynb,
tests/python/accparse.ipynb, tests/python/automata.ipynb,
tests/python/product.ipynb, tests/python/randaut.ipynb: Adjust test
cases.
spot::mark_t::sets() was modified so that it now returns an iterable
object rather than an std::vector<unsigned>.
* NEWS: Mention the modification.
* python/spot/impl.i: Declares mark_container as iterable to SWIG.
* spot/parseaut/parseaut.yy: Adapts to the modification.
* spot/twa/acc.hh: Implement the modification.
* tests/python/acc_cond.ipynb: Adapts to the modification.