scanner: Clean up non-destructive rescan

Fix several issues with the non-destructive rescan functionality.
Most of these issues also affected inotify scanning as well.  These
include annoying debug messages, adding album art for files that we
aren't supposed to be scanning anyway, incrementing the UpdateID when no
changes were made to the database, and other smaller issues.

scanner_sqlite.h

@@ -79,7 +79,8 @@ char create_playlistTable_sqlite[] = "CREATE TABLE PLAYLISTS ("
 					"NAME TEXT NOT NULL, "
 					"PATH TEXT NOT NULL, "
 					"ITEMS INTEGER DEFAULT 0, "
-					"FOUND INTEGER DEFAULT 0"
+					"FOUND INTEGER DEFAULT 0, "
+					"TIMESTAMP INTEGER DEFAULT 0"
 					");";
 
 char create_settingsTable_sqlite[] = "CREATE TABLE SETTINGS ("