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. 
@kmike thanks for clearing up. I didn't expect a huge number here, so I thought a list is sufficient, but absolutely got your point. 
It seems to force an iterator in both py2 and py3 would be best in this case. IMHO the try.. import method suggested by @dangra seems to solve this problem in a nice way without having new dependencies on external libraries.