Add failing test for #459
Add failing test for #459

Reproduces the original issue.

When I upload with requests.put(...) an open file
handle and simultaneously enable retries, urllib3
fails as it tries to retry upload without seeking
the file object.

Critically content-length needs to be set to
reproduce failure; otherwise data corruption will
occur as only partial content will be uploaded!

Thanks to @sigmavirus24 for continued support
with this issue.

Disassem/urllib3,Lukasa/urllib3,urllib3/urllib3,Disassem/urllib3,Lukasa/urllib3,urllib3/urllib3,sigmavirus24/urllib3,sigmavirus24/urllib3