Fixes for bug - Cookie retrieval for hosts with port + unittests for the...

Scrapy currently fails to supply cookies for hosts with port. This pull request aims to fix this.

Related Issue : https://github.com/scrapy/scrapy/issues/351

Excerpt from Browser Security Handbook : http://code.google.com/p/browsersec/wiki/Part2#Same-origin_policy_for_cookies - "Scope: by default, cookie scope is limited to all URLs on the current host name - and not bound to port or protocol information."