lalr1.cc: also handle syntax_error when calling yylex.

* data/lalr1.cc (parse): Catch syntax_error around yylex and
	forward them to errlab1.
	* tests/c++.at (Syntax error as exception): Check support for
	syntax exceptions raised by the scanner.
	* NEWS, doc/bison.texinfo: Document it.

tests/c++.at

@@ -492,9 +492,12 @@ item:
 int
 yylex (yy::parser::semantic_type *)
 {
-  static char const *input = "as";
+  // 's': syntax error, 'l': lexical error.
+  static char const *input = "asal";
   switch (int res = *input++)
   {
+    case 'l':
+      throw yy::parser::syntax_error("invalid character");
     default:
       return res;
   }
@@ -520,6 +523,8 @@ AT_COMPILE_CXX([[input]])
 AT_PARSER_CHECK([[./input]], [[0]], [[]],
 [[error: invalid expression
 caught error
+error: invalid character
+caught error
 ]])
 
 AT_CLEANUP