This patch introduces buffered I/O to rrdcached. Now, rrdcached can

This patch introduces buffered I/O to rrdcached.  Now, rrdcached can
interpret as many commands as arrive in a single read(), and it will use
fewer write()s when there are multiple output lines.

All routines now pass around listen_socket_t objects instead of file
descriptors.

All I/O is now contained in two routines.  It's no longer necessary to
specify the line count in multi-line outputs, since that is calculated
automatically.

This is the foundation for accepting batched commands.
-- kevin brintnall

git-svn-id: svn://svn.oetiker.ch/rrdtool/trunk@1580 a5681a0c-68f1-0310-ab6d-d61299d08faa