cleanup script for 2.1 stores

Here is a small script to run after upgrading from 2.0 to 2.1, it will
clean the main index and remove all unknown entries.
Of course it is an ugly script using sh and pushing sed to its limit (you
probably will have to use GNU sed, just set the environment variable SED
to the right version of sed).
It would have been better to write it in Java or even in perl, but sh and
sed rules ;)

      /\          - Yves Lafon - World Wide Web Consortium - 
  /\ /  \        Architecture Domain - Jigsaw Activity Leader
 /  \    \/\    
/    \   /  \   http://www.w3.org/People/Lafon - ylafon@w3.org