* Fixed problem with Alt key where certain keys get locked down

* Fixed econet station allocation on PCs with multiple network
interfaces/cards (thanks to Sam Skivington).

* Added keyboard shortcuts for Quicksave (keypad /) & Quickload (keypad *).
Quicksave now keeps the last 10 quicksave files so you can go back to an
earlier state using the load state menu option.

* Changed to ignore DirectX errors during screen update. Stops BeebEm
reporting an error when switching between a full and non-full screen mode
instances of BeebEm. DirectX appears to sort itself out after a second
or two!