Handle non-chunked body in AWS in presence of 'transfer-encoding' as 'chunked'

[daniel-ac-martin]

Performs a sanity check prior to parsing chunked bodies, to protect cases where the body is in fact NOT chunked despite having headers['transfer-encoding'] set to chunked.

Addresses: #308

Also:

• Makes a fix to an existing test
• Removes the transfer-encoding header

Adds failing tests prior to fixes to those tests.