upgrade files should use $db

Signed-off-by: emanuele <emanuele45@gmail.com>
Make upgrade.php able to distinguish a bit more effectively between SMF and Elk

Signed-off-by: emanuele <emanuele45@gmail.com>
If index.php checks for a file that exists only in Elk it can better recognize if there are leftovers from SMF upgrade

Signed-off-by: emanuele <emanuele45@gmail.com>
Merge pull request #953 from emanuele45/upgrade_quick

Upgrade quick