support Transfer-Encoding: chunked request body in conjunction with
server.stream-request-body = 0
dynamic handlers will still return 411 Length Required if
server.stream-request-body = 1 or 2 (!= 0)
since CGI-like env requires CONTENT_LENGTH be set
(and mod_proxy currently sends HTTP/1.0 requests to backends,
and Content-Length recommended for robust interaction with backend)
"request: support Chunked Transfer Coding for HTTP PUT"