List date when package first seen to need upgrade

List date when package first seen to need upgrade

Keeps a file in current dir with lines like
  bagel:xpdf 2012-05-01
to indicate that package was first seen to need upgrade on
that date. When new versions arrive, the date stays the same.
When the package gets updated, the noticeis removed from the file
(and nothing is shown for it on the page). When a new version
becomes available, notices the date again. Displays a plain '*'
for packages that were pending from before we started tracking
(which is today)