stength: fix detection of terminal automata

Fixes issue #553.

* spot/twaalgos/strength.cc (is_type_automaton): Make sure an
accepting SCC is not followed by a rejecting one.
(is_terminal_automaton): Mark the third-argument version deprecated.
* spot/twaalgos/strength.hh: Adjust.
* spot/twaalgos/couvreurnew.cc: Remove the inappropriate terminal
optimization.
* bin/ltlfilt.cc, spot/tl/hierarchy.cc, spot/twaalgos/gfguarantee.cc,
tests/core/ikwiad.cc: Remove usage of the third argument of
is_terminal_automaton.
* tests/core/readsave.test, tests/core/strength.test: Adjust test
cases.
* NEWS: Mention the bug.

tests/core/ikwiad.cc

@@ -1368,8 +1368,7 @@ checked_main(int argc, char** argv)
                 }
               else
                 {
-                  bool g = is_terminal_automaton(ensure_digraph(a),
-                                                 nullptr, true);
+                  bool g = is_terminal_automaton(ensure_digraph(a));
                   bool s = is_safety_automaton(ensure_digraph(a));
                   if (g && !s)
                     {

tests/core/readsave.test

@@ -826,7 +826,7 @@ test `autfilt --is-terminal -c output4` = 0
 
 sed 's/\[0\]/[t]/g' expect4 > output4d
 test `autfilt -B --small output4d | autfilt --is-terminal -c` = 1
-test `autfilt --is-terminal -c output4d` = 0  # FIXME: Issue #553
+test `autfilt --is-terminal -c output4d` = 1    # Issue #553
 
 autfilt -B -Hv --small input4 >output5
 cat >expect5<<EOF

tests/core/strength.test

@@ -679,7 +679,7 @@ AP: 1 "a"
 acc-name: Buchi
 Acceptance: 1 Inf(0)
 properties: trans-labels explicit-labels trans-acc complete
-properties: deterministic very-weak
+properties: deterministic terminal very-weak
 --BODY--
 State: 0
 [t] 0