When the browser is loading the diffs from the RB server, it can sometime
fail to do so especially if the RB server is behind a firewall and the
access has to go through a proxy.
The page on the browser shows that the file is being loaded but there is an
error later on in the page where the file is actually going to be shown.
Something like this is out of RB's control so we should allow the user to
reload just that file. Currently the only way to do this is to reload the
entire page which can take a long time.