ats has problems handling if-none-match requests for compressed objects

When using the compress plugin, ats appends the “-df” suffix to the Etag for the generated compressed object.

However, when ats responds to the if-none-match conditional request on the compressed object, it always uses the original Etag（without "-df" suffix）, so it cannot return 304 properly.


currently i use lua plugin to get a workaround.

`local c_req_hdr = ts.client_request.header['If-None-Match']`
`ts.client_request.header['If-None-Match'] = string.gsub(c_req_hdr, "-df", "")`