gitweb: refactor If-Modified-Since handling
The current gitweb only generates Last-Modified and handles
If-Modified-Since headers for the git_feed action. This patch breaks
the Last-Modified and If-Modified-Since handling code out from
git_feed into a new function exit_if_unmodified_since. This makes the
code easy to reuse for other actions.
Only gitweb actions which can easily calculate a modification time
should use exit_if_unmodified_since, as the goal is to balance local
processing time vs. upload bandwidth.
Signed-off-by: W Trevor King <wking@drexel.edu>
Acked-by: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>