Change #1986. Added support of _renderItem in CJuiAutoComplete

Issue #1986
Added support of _renderItem to be able to use custom renderer like this,
```
 $( "#ID" ).autocomplete({
minLength: 2,
source: customSource,
}).data( "autocomplete" )._renderItem = function( ul, item ) {
return $( "<li>" )
.data( "item.autocomplete", item )
.append( "<a>" + item.label + "<br>" + item.desc + "</a>" )
.appendTo( ul );
};
});
```
see http://jqueryui.com/autocomplete/#custom-data