update_render.sh doesn't cope well with downloads at around the time that Geofabrik files are updated #18
Description
In the most recent example of this I had an old "great-britain_somedate.osm.pbf" and as part of "update_render.sh" downloaded "isle-of-man_somedate.osm.pbf" et al as well. However, the "great-britain" file actually contained data from a day earlier. What happened was that a Garmin process ran "at about the Geofabrik file change time" and I ended up with "yesterday's" file with "today's" date.
This isn't a bug at the Geofabrik end since the updates there (to several files and web pages) can't be atomic.
Instead I should check here that when I "think I have a file" that (perhaps) the md5sum matches and (perhaps) that the files being merged all have the same date (currently all files are checked to be "the latest" date, which may be different if a download is run at around the time that the Geofabrik data is updated.