Rob W. W. Hooft's spelling fixes for the Library Reference. I hope

Rob W. W. Hooft's spelling fixes for the Library Reference. I hope
SourceForge doesn't choke on this batch :-)

I'm not entirely sure this is 100% correct. The patch changes an
\index{persistency} to \index{presistence}, and I don't know what \index{}
does. But it seems to do so persi--er, consistently, so I hope it isn't a
problem.