monitor: fix -MD/-M difference in property output

Fixes #241.

* spot/twaalgos/postproc.cc: Use the deterministic monitor if it
has as many states as the non-deterministic one.
* spot/twaalgos/minimize.cc (minimize_monitor): Quickly check
for terminal automata.
* spot/twaalgos/stripacc.cc: Set the weak property.
* spot/twaalgos/stripacc.hh: Improve documentation.
* tests/core/monitor.test, tests/core/sbacc.test: Update.
* NEWS: Mention the issue.

tests/core/monitor.test

@@ -44,7 +44,7 @@ digraph G {
 }
 EOF
 
-expect ltl2tgba --monitor a GFa --hoa<<EOF
+expect ltl2tgba --monitor a GFa Ga --hoa<<EOF
 HOA: v1
 name: "a"
 States: 2
@@ -68,11 +68,24 @@ AP: 0
 acc-name: all
 Acceptance: 0 t
 properties: trans-labels explicit-labels state-acc complete
-properties: deterministic stutter-invariant
+properties: deterministic stutter-invariant terminal
 --BODY--
 State: 0
 [t] 0
 --END--
+HOA: v1
+name: "Ga"
+States: 1
+Start: 0
+AP: 1 "a"
+acc-name: all
+Acceptance: 0 t
+properties: trans-labels explicit-labels state-acc deterministic
+properties: stutter-invariant weak
+--BODY--
+State: 0
+[0] 0
+--END--
 EOF
 
 # Completing a monitor can produce a Büchi automaton.
@@ -85,7 +98,7 @@ AP: 1 "a"
 acc-name: Buchi
 Acceptance: 1 Inf(0)
 properties: trans-labels explicit-labels state-acc complete
-properties: deterministic stutter-invariant inherently-weak
+properties: deterministic stutter-invariant weak
 --BODY--
 State: 0 {0}
 [0] 0

tests/core/sbacc.test

@@ -141,7 +141,7 @@ Start: 0
 AP: 1 "a"
 acc-name: all
 Acceptance: 0 t
-properties: trans-labels explicit-labels state-acc deterministic
+properties: trans-labels explicit-labels state-acc deterministic weak
 --BODY--
 State: 0
 [0] 1