#10 Behavior to enable objective evaluation of "Get Dijjer" page

[Holmes Wilson]

This is reallly a feature request, not a bug. There are some small
additions to the Dijjer client that would give us concrete data on
how successful the 'Get Dijjer' page is at facilitating a) Dijjer
installation and b) downloading the desired file. This is important
because otherwise the design of the 'Get Dijjer' page
(potentially the weakest link in the chain) will just be based on
guesses as to what's the most usable. If we have data, then we
know how good it is and when our changes make it better or
worse.

We already know how many people arrive at the "Get Dijjer" page.
So the next thing we need to know is: how many of those people
a) install Dijjer and b) go back to get the file they wanted. Once
we have those numbers we have a success rate.

One way to get those numbers is to have the Dijjer client notify
dijjer.org when it installs successfully and then when it downloads
its first file. There's probably a better way.