checkupdates: don't auto update to older versions

If for whatever reason the update check results in an older version that we
didn't package, don't "update" to that version if we already packaged newer
versions.

fdroidserver/checkupdates.py

@@ -474,6 +474,9 @@ def checkupdates_app(app, first=True):
                 if not latest or int(build['vercode']) > int(latest['vercode']):
                     latest = build
 
+            if int(latest['vercode']) > int(app['Current Version Code']):
+                logging.info("Refusing to auto update, since the latest build is newer")
+
             if not gotcur:
                 newbuild = latest.copy()
                 if 'origlines' in newbuild: