Do not compute |resultIndex| for "rule" nodes

Computing |resultIndex| for their expressions is enough.

src/compiler/passes/allocate-registers.js

@@ -42,7 +42,6 @@ PEG.compiler.passes.allocateRegisters = function(ast) {
     grammar:
       function(node, index) {
         each(node.rules, function(node) {
-          node.resultIndex = index;
           compute(node, index);
         });
       },
@@ -51,7 +50,7 @@ PEG.compiler.passes.allocateRegisters = function(ast) {
       function(node, index) {
         var depth;
 
-        node.expression.resultIndex = node.resultIndex;
+        node.expression.resultIndex = index;
 
         depth = compute(node.expression, index);
 

src/compiler/passes/generate-code.js

@@ -567,10 +567,10 @@ PEG.compiler.passes.generateCode = function(ast, options) {
             '    ',
             '    cache[cacheKey] = {',
             '      nextPos: #{posClone("pos")},',
-            '      result:  #{r(node.resultIndex)}',
+            '      result:  #{r(node.expression.resultIndex)}',
             '    };',
             '  #end',
-            '  return #{r(node.resultIndex)};',
+            '  return #{r(node.expression.resultIndex)};',
             '}'
           ],
           named: [