urlsum.txt: summary of results
   urllog.txt: log of progress
   urlok.html: found  77 urls: were ok
urlmoved.html: -----   4 urls: moved
 urlhost.html: ERROR   8 hosts: failed
 urlfail.html: ERROR  26 urls: failed
urlfailX.html: ERROR  26 urls: failed (cross referenced)
urlfailF.html: ERROR  17 files with failed urls
 urlskip.html: warn    1 url: not checked