This is a maintenance release of 1.6 series, fixing the following bugs.

• [fastcgi][proxy] fix double-free issue during configuration phase #723 (Kazuho Oku)
• [proxy] fix response getting truncated when neither content-length nor transfer-encoding is used #725 (Kazuho Oku)
• [websocket] fix crash when access-log is enabled #698 (Shota Fukumori)