Check the content-encoding header more carefully

[indust]

2016/03/27 14:41:47 [debug] 5476#0: *16 http proxy status 200 "200 OK"
2016/03/27 14:41:47 [debug] 5476#0: *16 http proxy header: "Content-Type: text/css; charset=utf-8"
2016/03/27 14:41:47 [debug] 5476#0: *16 http proxy header: "Access-Control-Allow-Origin: *"
2016/03/27 14:41:47 [debug] 5476#0: *16 http proxy header: "Timing-Allow-Origin: *"
2016/03/27 14:41:47 [debug] 5476#0: *16 http proxy header: "Content-Encoding: identity"
2016/03/27 14:41:47 [debug] 5476#0: *16 http proxy header: "Content-Length: 273"
2016/03/27 14:41:47 [debug] 5476#0: *16 http proxy header: "Expires: Sun, 27 Mar 2016 06:41:47 GMT"
2016/03/27 14:41:47 [debug] 5476#0: *16 http proxy header: "Date: Sun, 27 Mar 2016 06:41:47 GMT"
2016/03/27 14:41:47 [debug] 5476#0: *16 http proxy header: "Cache-Control: private, max-age=86400"
2016/03/27 14:41:47 [debug] 5476#0: *16 http proxy header: "X-Content-Type-Options: nosniff"
2016/03/27 14:41:47 [debug] 5476#0: *16 http proxy header: "X-Frame-Options: SAMEORIGIN"
2016/03/27 14:41:47 [debug] 5476#0: *16 posix_memalign: 0000000001A4CA80:4096 @16
2016/03/27 14:41:47 [debug] 5476#0: *16 http proxy header: "X-XSS-Protection: 1; mode=block"
2016/03/27 14:41:47 [debug] 5476#0: *16 http proxy header: "Server: GSE"
2016/03/27 14:41:47 [debug] 5476#0: *16 http proxy header done
2016/03/27 14:41:47 [warn] 5476#0: *16 http subs filter header ignored, this may be a compressed response. while reading response header from upstream, client: 114.65.*.*, server: gfonts-backend.example.com, request: "GET /css?family=Source+Sans+Pro HTTP/2.0", upstream: "https://203.208.40.37:443/css?family=Source+Sans+Pro", host: "gfonts-backend.example.com"

The response with default content encoding(identity) which means no compression should not be bypass. https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Encoding

[yaoweibin]

LGTM