bug for nested variable not usable in 'for' tag

There is no need to validate the property "name" of variable 'operand2', because the variable name will be instead as '__loopIter'.

The validation cause syntax like '<% for item in pord.items %>' throw an error, which are availiable in fact.

lib/tags/for.js

@@ -22,10 +22,6 @@ module.exports = function (indent, parser) {
     throw new Error('Invalid arguments (' + operand1 + ') passed to "for" tag');
   }
 
-  if (!helpers.isValidName(operand2.name)) {
-    throw new Error('Invalid arguments (' + operand2.name + ') passed to "for" tag');
-  }
-
   operand1 = helpers.escapeVarName(operand1);
 
   loopShared = 'loop.index = __loopIndex + 1;\n' +