.netrc settings shouldn't blow away explicit auth settings on a session
Add test to verify .netrc authentication behavior.

Here's what should happen:

- If no credentials are given, use netrc if there's a netrc entry.
- If credentials are given, they should override netrc.
Remove urllib3-specific kwargs from general code
Changed the "im_used" informational status code for the value given by IANA (226)

See RFC 3229 at http://tools.ietf.org/html/rfc3229#section-10.4.1 and HTTP status codes at http://www.iana.org/assignments/http-status-codes/http-status-codes.xhtml
Set 208 status_code to "already_reported"
Merge pull request #1456 from phndiaye/master

Changed the "im_used" informational status code for the value given by IANA (226)
Merge pull request #1441 from Lukasa/1395

Remove urllib3-specific kwargs from non-urllib3 branch.
Merge pull request #1439 from voberoi/master

Make sure netrc doesn't override any authentication settings explicitly set by the client