Add a paramter for maximum CLI buffer size and use it both in child

Add a paramter for maximum CLI buffer size and use it both in child
and manager.  To take effect, it must be specified with -p on the
command line.

Use VLU for managers CLI handling.

Note CLI connection events on stderr.

git-svn-id: svn+ssh://projects.linpro.no/svn/varnish/trunk@2477 d4fa192b-c00b-0410-8231-f00ffab90ce4