Author: Alex Rousskov <rousskov@measurement-factory.com>

Author: Alex Rousskov <rousskov@measurement-factory.com>
Bug 3016: HTTP/1.1 compliance: default keep-alive for 1.0/1.1 clients.

aka. NTLM Authentication with Java UA + SSL Problem
Moved httpMsgIsPersistent(version, headers) to HttpMsg::persistent(void).

This move makes it clear that the logic applies only to the message being
examined and not some irrelevant information such as HTTP version supported
by Squid.

Side-effects:

 - In v3.2, Squid stops using persistent connections with HTTP/1.0 clients
   that do not send "Connection: keep-alive".

 - In v3.1, Squid starts using persistent connections with HTTP/1.1 clients
   that do not send "Connection: close".

 - HttpReply now sets HttpMsg::http_ver member. It is not clear whether
   that member was ever used for HttpReplies though.