update vendored urllib3
add 'max_redirects' to Session's __attrs__ to ensure proper serialization of Session
Merge pull request #1270 from makto/add_attr

add 'max_redirects' to Session's __attrs__
Merge pull request #1267 from sigmavirus24/master

One last pull request before 1.2 ideally
fix syntax error
Merge pull request #1268 from t-8ch/update_urllib3

update vendored urllib3
v1.2.0
Merge remote-tracking branch 'origin/master'
is should not be used for comparing numbers
Fixed typos
fix tiny typo in HISTORY.rst
Merge pull request #1276 from alex/patch-1

is should not be used for comparing numbers
Merge pull request #1277 from pborreli/typos

Fixed typos
Merge pull request #1278 from t-8ch/patch-1

fix tiny typo in HISTORY.rst
Fix for the issue https://github.com/kennethreitz/requests/issues/1280
Merge pull request #1281 from KamilSzot/Issue_kennethreitz_requests_issues_1280

Fix for the issue https://github.com/kennethreitz/requests/issues/1280
Revert "Fix for the issue https://github.com/kennethreitz/requests/issues/1280"

This reverts commit ca0aea640d0cce01c126220b74362c9014cabbd6.
Closes #1280

Correct the doc-string for Session#request that I copied without thinking
about.