Added CURLOPT_TRANSFER_ENCODING as the option to set to request Transfer
Encoding in HTTP requests (if built zlib enabled). I also renamed
CURLOPT_ENCODING to CURLOPT_ACCEPT_ENCODING (while keeping the old name
around) to reduce the confusion when we have to encoding options for
HTTP.
--tr-encoding is now the new command line option for curl to request
this, and thus I updated the test cases accordingly.
When TE: is inserted in the request, we must add a "Connection: TE" as
well to be HTTP 1.1 compliant. If a custom Connection: header is passed
in, we must use that and only append TE to it. Test case 1125 verifies
TE: + custom Connection:.
