sccfilter: some inherently-weak automata should have t acceptance

* spot/twaalgos/sccfilter.cc: If an inherently-weak automaton has
no rejecting cycle, reduce its acceptance to t instead of Büchi.
* spot/twa/acc.hh (operator==, operator<): Fix comparisons of
true acceptances.
* NEWS: Mention these two changes.
* spot/twaalgos/sccfilter.hh: Update documentation.
* spot/twaalgos/determinize.cc (tgba_determinize): The call
to scc_filter assume that the input BA is never reduced to t
acceptance.  Call scc_filter with an extra option to ensure that.
* spot/twaalgos/postproc.cc (do_scc_filter): Adjust to add the
extra option when we want to build Büchi or coBuchi.
(ensure_ba): Don't mark trivial SCCs as accepting.
* tests/core/complement.test, tests/core/dstar.test,
tests/core/ltlsynt.test, tests/core/readsave.test,
tests/core/wdba2.test, tests/python/_product_susp.ipynb,
tests/python/automata-io.ipynb, tests/python/dualize.py,
tests/python/highlighting.ipynb, tests/python/intrun.py,
tests/python/setacc.py, tests/python/simstate.py,
tests/python/stutter-inv.ipynb, tests/python/zlktree.py: Adjust test
cases.

tests/python/intrun.py

@@ -52,27 +52,27 @@ tc.assertEqual(str(r), """Prefix:
   1
   |  a
   0
-  |  1	{0}
+  |  1
   0
-  |  a	{0}
+  |  a
 Cycle:
   0
-  |  1	{0}
+  |  1
 """)
 tc.assertEqual(r.as_twa().to_str(), """HOA: v1
 States: 4
 Start: 0
 AP: 1 "a"
-acc-name: Buchi
-Acceptance: 1 Inf(0)
+acc-name: all
+Acceptance: 0 t
 properties: trans-labels explicit-labels state-acc deterministic
 --BODY--
 State: 0
 [0] 1
-State: 1 {0}
+State: 1
 [t] 2
-State: 2 {0}
+State: 2
 [0] 3
-State: 3 {0}
+State: 3
 [t] 3
 --END--""")