Avoid causing libcurl to use chunked Transfer-Encoding for POST bodies

[mbaynton]

For #154 I had success by preventing the recorder proxy from employing chunked Transfer-Encoding. It seemed like connect et. al just don't do well when given properly formed chunked requests.

Here's someone driving libcurl with PHP who had a similar issue: php/php-src#8165
Based on the age of that, I wonder if cURL going to chunked Transfer-Encoding when it is uploading from CURLOPT_READFUNCTION and the length hasn't been provided ahead of time is a newer behavior.

Disclaimer: I don't really write much R 🙃

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