Fixed #23620 -- Used more specific assertions in the Django test suite.
Fixed #18523 -- Added stream-like API to HttpResponse.

Added getvalue() to HttpResponse to return the content of the response,
along with a few other methods to partially match io.IOBase.

Thanks Claude Paroz for the suggestion and Nick Sanford for review.
Refactored URLValidator tests by moving URLs to text files.
Fixed #20003 -- Improved and extended URLValidator

This adds support for `user:password` in URLValidator supported URLs.

Additionally, the test suite has been improved by adding test URLs from
http://mathiasbynens.be/demo/url-regex (with a few adjustments, like
allowing local and reserved IPs).

The previous URL validation RegEx failed this test suite on 13
occasions, so I also updated the URLValidator based on
https://gist.github.com/dperini/729294 to correctly validate all URLs in
the test suite. Among other improvements, this also adds support for
IPv4 mapped IPv6 addresses like `::ffff:192.0.2.128`.