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. 
can you explain why it is that bad? I might not see it..
I think it should actually also be save to remove the list() entirely. since it is in a for loop anyway it doesn't matt if it is an iterator (py3) or a list (py2). As I said before, i've kept the list() to have the same behaviour (list) in both python versions.