Split keepalive from pipelining in HTTP connections (bug https://bugs.ec...

...lipse.org/bugs/show_bug.cgi?id=434402). A new property 'pipelining' is added to HttpClient to disable HTTP pipelining (by default, pipelining is true to maintain backwards compatibility)
By defaulting this to true all non-Java clients are forced into pipelining enabled. An http server that closes it's connections will cause any pipelined request after the first to fail with a timeout.  Since the pipelining support is effectively broken shouldn't this have been defaulted to false?