Add support for the {SERE}! PSL operator.

* src/ltlparse/ltlscan.ll: Recognize }!.  Also remove
five duplicate rules.
* src/ltlparse/ltlparse.yy: Build {r}<>->1 when parsing {r}!.
* src/ltlvisit/tostring.cc: Print {r}! instead of {r}<>->1.
* src/ltltest/tostring.test, src/ltltest/equals.test:
Add more tests.

src/ltlparse/ltlparse.yy

@@ -83,6 +83,7 @@ using namespace spot::ltl;
 %token START_RATEXP "RATEXP start marker"
 %token PAR_OPEN "opening parenthesis" PAR_CLOSE "closing parenthesis"
 %token BRACE_OPEN "opening brace" BRACE_CLOSE "closing brace"
+%token BRACE_BANG_CLOSE "closing brace-bang"
 %token OP_OR "or operator" OP_XOR "xor operator"
 %token OP_AND "and operator" OP_SHORT_AND "short and operator"
 %token OP_IMPLIES "implication operator" OP_EQUIV "equivalent operator"
@@ -627,6 +628,10 @@ subformula: booleanatom
 	      { missing_right_binop($$, $1, @2,
 				"existential non-overlapping concat operator");
 	      }
+            | BRACE_OPEN rationalexp BRACE_BANG_CLOSE
+	      /* {SERE}! = {SERE} <>-> 1 */
+	      { $$ = binop::instance(binop::EConcat, $2,
+				     constant::true_instance()); }
 ;
 
 %%