Check staging locations

For every file ref in foxml that starts with "tag:", check that we recognize the staging area and that we can connect to it. Tries to connect the staging area twice, a second time after 5 second delay. This is to see if the first access attempt wakes the mount point, since we've seen it do that. Once a staging area is connected, it doesn't get polled again. (Stages object stored connected state.)
Are tagged file references the only ones that need to be checked for?