HTTPClientSession and DEFAULT_KEEP_ALIVE_TIMEOUT

[micheleselea]

In HTTPClientSession, when in keepalive, we use the default 8 seconds DEFAULT_KEEP_ALIVE_TIMEOUT to check with _lastRequest and control if the connection has to reconnect. The _lastRequest is updated on sendRequestImpl()
I was thinking that probably we should update _lastRequest even after response received, otherwise if a response last 8 seconds you will always end up with a reconnection make the keep alive setting useless: it's just something I asking myself, what do you think about?