CPC 464 Rom is running disks by default

[ColinPitrat]

From issue #227

Running cap32 with cpc464 model selected, it should look for tape by default (e.g. when running cat) but is looking for disk.

[ColinPitrat]

Checked in the first commit on git (https://github.com/ColinPitrat/caprice32/commit/66a4a7af9125d2f20111493d13537db9f9cb6ff5) and this was already the case

[ColinPitrat]

This comes from the fact that amsdos.rom is loaded.

As said in https://en.wikipedia.org/wiki/AMSDOS:

AMSDOS first appeared in 1984 on the CPC 464, with added 3 inch disk drive, and then on the CPC 664 and CPC 6128. Relatively fast and efficient for its time, AMSDOS was quicker and more effective than most of its contemporaries.

Or here:

AMSDOS could be run only with Amstrad's 3" floppy disk drive.

So we shouldn't add amsdos.rom with CPC464.

Now the difficulty is that these are 2 orthogonal settings: which model is in use and which ROMs are configured. Ideally we'd like to have this AMSDOS ROM removed for the 464 unless it's been specified by the user.

If we only consider configuration editing from the UI, that's easy. When you switch to 464, remove the amsdos.rom from slot 7 if present.

However I also want to preserve manual editing of the cap32.cfg file.

[ColinPitrat]

The solution in https://github.com/ColinPitrat/caprice32/commit/61f6cb0ecdef8008ee1aba4d93927d65ba8f77de consists in:

• introducing a DEFAULT keyword for Rom 7 which allows to specify that we want the default ROM
• if using 464, DEFAULT means no ROM, if using 664 or 6128 it means amsdos.rom
• if a user overrides DEFAULT with a particular value (for example amsdos.rom) then the override is kept across model changes

I think it's unlikely a user would override the ROM 7 and be hurt by that later.