Review of 1.0.3: names a snapshot cannot hold, restore-directory errors under salvage, browse speed

- Leave out and report a file or folder whose name a snapshot cannot hold
- A staging write failure stops a full restore under --salvage
- Browse reuses its repository; empty folders read along with the entries
- Keep leases alive while empty folders are created; exact-prefix empty folder is the target
- Clean up tables that were partly created or before the transaction started
- Bin: no empty message after a read error; longer pages

lib/Controller/AdminApiController.php

@@ -83,7 +83,7 @@ final class AdminApiController extends Controller {
 	/** Seconds of backup work one tick() does: well within a normal web request. */
 	public const TICK_SECONDS = 10.0;
 	/** Seconds one request for the Bin reads, before the page shows how far it is and asks for more. */
-	private const TRASH_PAGE_SECONDS = 2.0;
+	private const TRASH_PAGE_SECONDS = 5.0;
 
 	/**
 	 * Move running backups forward from the open admin page, when background jobs do not run on a