VSL_H_Print() prints a 'b' in the third column for backend-related log

VSL_H_Print() prints a 'b' in the third column for backend-related log
entries, a 'c' for client-related log entries, and a ' ' for everything
else (CLI Ping for instance).  This makes it hard to process logs with
awk or similar tools, since the number of columns varies.  Therefore,
change the character used for non-backend-or-client log entries to '-'.

git-svn-id: svn+ssh://projects.linpro.no/svn/varnish/trunk@2591 d4fa192b-c00b-0410-8231-f00ffab90ce4