fixing illegal return statement in nw-checked

Fixing Issue #98. Remove return statement if it is returned from parseExpression. Same approach as in getValueBinding:
``` javascript
getValueBinding: function(model, el, bindings, loopStack, attrVal) {
  var expr = nweb.parseExpression(model, attrVal, loopStack);
  var exprWithReturn = expr;

  if (expr.indexOf("return ") == 0)
    expr = expr.slice(7);
//...
},
```