BUG/MEDIUM: http-ana: Properly detect client abort when forwarding response (v2)

BUG/MEDIUM: http-ana: Properly detect client abort when forwarding response (v2)

The first attempt to fix this issue (c672b2a29 "BUG/MINOR: http-ana:
Properly detect client abort when forwarding the response") was not fully
correct and could be responsible to false report of client abort during the
response forwarding. I guess it is possible to truncate the response.

Instead, we must also take care that the client closed on its side, by
checking SC_FL_EOS flag on the front SC. Indeed, if the client has aborted,
this flag should be set.

This patch should be backported as far as 2.8.