#517 Don't treat 128K .sna files as Pentagon files

[Joerg Pleumann]

This has been debated on the mailing list several months ago and my impression was that there might be consensus for a change.

Right now, when loading a 128 .sna file, Fuse does that in Pentagon mode. If those ROMs are not installed, it fails. The 128K snapshot format is not inherently tied to the Pentagon, though. It's just an extension of the 48K .sna format to those additional memory banks of the 128K.

I'm suggesting to either treat those .sna files as "plain" 128K by default, or fall back to 128K if the Pentagon ROMs are not installed (which would not break any existing behavior), or introduce a setting somewhere.