handlers can read response before sending req body (fixes #131, #2566)
dynamic handlers mod_fastcgi, mod_scgi, and mod_proxy can now read
response from backend prior to finishing sending request body.
If the backend closes the connections (or shuts down socket write
end so that lighttpd read() 0 to indicate EOF), then lighttpd will
abort attempting to send request body to backend.
x-ref:
"mod_fastcgi should handle "quick" responses"
https://redmine.lighttpd.net/issues/2566
"FastCGI FCGI_STDOUT before FCGI_STDIN bug"
https://redmine.lighttpd.net/issues/131