* spot/twa/twagraph.hh, spot/twaalgos/are_isomorphic.cc,
spot/twaalgos/canonicalize.cc, spot/twaalgos/couvreurnew.cc,
spot/twaalgos/cycles.cc, spot/twaalgos/degen.cc,
spot/twaalgos/determinize.cc, spot/twaalgos/isunamb.cc,
spot/twaalgos/isweakscc.cc, spot/twaalgos/mask.hh,
spot/twaalgos/minimize.cc, spot/twaalgos/product.cc,
spot/twaalgos/randomize.cc, spot/twaalgos/sbacc.cc,
spot/twaalgos/sccfilter.cc, spot/twaalgos/simulation.cc:
Throw a runtime_error if the input is alternating.