Manual refresh of feeds and time left before next refresh

This patch adds a 'manual refresh' link to feed items when you have the 'administer feeds' privilege along with the time until the next update. Of course, you have to visit the feed node and hit refresh; simplefeed doesn't have a 'listing' of feeds like aggregator (yet?).

The patch was done in windows (with WinMerge) and I can't say I have much experience with this, so I hope its functional. Thanks for the great module m3avrck!