Updater: allow re-check after checking

When opening the activity update control panel, closing it once the list
of available updates has been presented, and then trying to open it again,
we would be in STATE_CHECKED and try to check for updates again
(i.e. refresh).

This was causing an UpdaterStateException even though we can and should
handle this simple refresh case.
Microformat update: fix size lookup handling

For a Downloader.get_size request, the size of the remote file is
passed in the result parameter. Not sure why we were trying to call
the result as if it were callable.

Fixes a failure to update activities using the microformat updater.