improve replay attacker, add deadlock tests

tests/no-deadlocks/t1-deadlock.pml

@@ -0,0 +1,21 @@
+chan c = [8] of { byte };
+byte q=1;
+
+init {
+c!5;
+c!5;
+c!5;
+}
+
+active proctype consume() {
+MAIN:
+  do 
+  :: c ? 5 -> goto PROC;
+  od
+PROC:
+  q=0;
+}
+
+ltl proc {
+  eventually (q == 0);
+}