Handle socket errors in iter_content
Replace setattr
Merge pull request #2148 from romanlevin/handle-socket-error-in-iter_content

Handle socket errors in iter_content
handle urllib3 api changes; closes #2045
Merge pull request #2153 from jschneier/master

handle urllib3 api changes; closes #2045
Allow fetching the session's sending parameters.

This will allow users using prepared requests to apply the environment
variables themselves before calling send.

Closes #1436