[perl #113552] duplicate rule/token names break grammar parsing

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# New Ticket Created by  diakopter 
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00:28 < diakopter> r: grammar A { token a { }; token a { } }
00:28 <+p6eval> rakudo 6ab416: OUTPUT«===SORRY!===␤Method 'match' not found for
                invocant of class 'String'␤at /tmp/TaBvwFfZ6b:1␤»

expected: a real error.