WarcMiddleware is adding a 'Host' header to requests, creating redicrt loops.

[esegal]

With warcmiddleware.py, doing 'scrapy fetch http://www.pcaobus.org' I get a redirect loop.
I've isolated the problem to the line "headers.setdefault('Host', netloc)" in _warcrec_from_scrapy_request

When removing it everything seems to be working fine. Also - I think the middleware doesn't intend to change the headers, but it does.