Use If-Modified-Since Header when refreshing feeds
Use If-Modified-Since Header when refreshing feeds

Fetch feeds with the If-Modified-Since HTTP header set to the last refresh timestamp.
This should save us (and the feed providers) quite some traffic since we don't have the fetch the whole feed when the content hasn't changed

adscott/stringer,nibble/stringer,dandorman/stringer,nobuti/stringer,dperson/stringer,swanson/stringer,milandobrota/stringer,dandorman/stringer,thiagosil/stringer,jqr/stringer,run-project/stringer,mpraglowski/stringer,Koronen/stringer,Koronen/stringer,milandobrota/stringer,jeroenj/stringer,thiagosil/stringer,wwwjfy/stringer,dperson/stringer,jeroenj/stringer,jqr/stringer,wwwjfy/stringer,nobuti/stringer,InPermutation/stringer,jeroenj/stringer,geemus/stringer,dperson/stringer,mpraglowski/stringer,geemus/stringer,nobuti/stringer,adscott/stringer,milligramme/stringer,nibble/stringer,jqr/stringer,lodestone/stringer,nibble/stringer,swanson/stringer,bkbabydp/stringer,swanson/stringer,Koronen/stringer,InPermutation/stringer,lodestone/stringer,swanson/stringer,dandorman/stringer,thiagosil/stringer,bkbabydp/stringer,milligramme/stringer,adscott/stringer,geemus/stringer,geemus/stringer,run-project/stringer,jqr/stringer,jeroenj/stringer,dperson/stringer,run-project/stringer,adscott/stringer,Koronen/stringer,nibble/stringer,mpraglowski/stringer,milligramme/stringer,milandobrota/stringer,InPermutation/stringer,lodestone/stringer