basic py3.3 compatibility while keeping py2.7 compatibility

makes the api callable from py2.x and py3.x. Since scrapy itself is not yet python3 compatible this might be still useful if one has a control application/api written in py3 which should be able to control scrapy crawlers. 
It's actually not necessary. I left it in, to avoid unexpected behaviour since py3 range returns an iterator while py2 range returns a list.