bandwidthd robust filesystem creation

Make the code that starts bandwidthd check for the correct dirs and symlinks, leave them alone if they are already there, and put them in place if they are missing. This fixes some places where some commands were generating "already exists" warnings, and generally makes sure that whatever someone does at the command line to mess with bandwidthd dirs and links, they will be put back when bandwidthd starts.
Merge pull request #392 from phil-davis/master

bandwidthd robust filesystem creation