#2 Force proxy refresh on .xml fetch

Greg Whiteley

I have a proxy server at work which is very agressive
with caching and sometimes refuses to notice when a
cached file changes. This can result in missing out on
podcasts (for up to a couple of months in one instance)
as the proxy always returns the old version.

This patch changes the fetching of the .xml/.rss (ie
not the content) to add the HTTP "Pragma: no-cache"
suggestion to the headers, to recommend that the proxy
re-fetch instead of returning the cached version.

A better long-term solution would be to change the HTTP
request structure for fetching the .xml/.rss files.
Where possible store (persistently) the following
returned headers from the last received update of a
.xml/.rss line

Last-Modified: Mon, 06 Mar 2006 01:39:40 GMT
ETag: "68aa67-6ad-99a56f00"

Then use
If-Modified-Since: Mon, 06 Mar 2006 01:39:40 GMT
If-None-Match: "68aa67-6ad-99a56f00"

HTTP headers to conditionally fetch changes (if any)
(and proxies that support HTTP/1.1 should always work
that properly (its in the standard)).

I've never written any python before so have not
attempted to add a GUI configuration parameter to
control this behaviour. Anyone wanting to volunteer?
I might take a look myself at some time but for now
this patch works for me.