add support for the HTTP/1.1 protocol which allows sockets to stay open.

This saves a lot of time in not having to open and setup sockets for
each request. They gain can be up to 100% or more.


git-svn-id: http://root.cern.ch/svn/root/trunk@19486 27541ba8-7e3a-0410-8455-c3a389f83636