Over the past while it has become increasingly obvious that it's
useful for as many responses as possible to carry a Last-Modified:
header. (The last straw was wanting Google's index to show
modification dates for DWiki pages.)
My reason for killing Last-Modified: was so that things like logging
in and logging out, which can't be reflected in the timestamp, would
still have conditional GETs be served new pages. But since the
conditional GET logic is in DWiki itself, I can have DWiki be
smarter about it.
DWiki now separates the page timestamp from the idea of whether the
page timestamp is reliable or simply vaguely useful information. The
page timestamp will always be served if it exists at all, but
conditional GETs only look at the page timestamp if it's reliable
(which means that if authentication is on, the answer is generally
'not').
This should work much better.