! Upgrade fixes

This fixes the following issues:
1. The upgrade script only tries CHMOD 777 if the custom av. directory isn't writable; should try 755 and 775 first since 777 isn't necessary in many cases.
2. The @ operator doesn't suppress errors when running the script via shell/command line, so don't try to rename/move files unless they exist.
3. Database error caused by attempting to drop a non-existent table.

Signed-off-by: Michael Eshom <oldiesmann@oldiesmann.us>