mod_speedyfeed is an Apache2 filter that implements the feed instance
manipulation method for RFC3229, as described by Bob Wyman in [1].

It detects content that's served up with a content type that indicates
that it's Atom and handles the If-Modified-Since and A-IM magic to only
send the needed bits of the feed down to the client.

Note that in order to build this you'll need a patched version of Apache2,
since the current version doesn't support the 226 status code.  Grab the
patch from the Apache Bugzilla at [2].

[1] - http://bobwyman.pubsub.com/main/2004/09/using_rfc3229_w.html
[2] - http://nagoya.apache.org/bugzilla/show_bug.cgi?id=31228