fix DSK device to deal with non-linkable file system about medley

[nbriggs]

For Medley: On a filesystem that doesn't support hard links at all, it reports a "File not found" error if creating the file would require hard linking a version. You can create a completely new file and it will create it as the unversioned name, but as soon as it would have to make links it fails. However, I think we'd get the desired effect if it renamed foo => foo.1 and wrote the new file as foo, then next rename would be foo => foo.2 and write foo again. You can experiment using a FAT formatted thumbdrive as your target -- it doesn't support hard links.

[masinter]

I think you need to store the "intended" version number in metadata somewhere.
let's suppose i do a makefile(foo) 5 times in a session. It writes versions 1 through 5.
now i 'thin' and delete version 4. You don't want the unadorned FOO to be treated as version 4 now.

[masinter]

This might be a separate issue but it's all tied up with DSK.c code -- how to emulate Interlisp versions with Git versioning.
Every time you write a file (even one opened in read-write mode?) it creates a new git checkin when you close the file.
The checkin has the version of the file as a tag.
files have as many versions as they have in GitHub. To convert a file name that uses the DSK method of filename.~version~
to the gitversioned method, convert the lowest version first (without

[masinter]

@nbriggs notes

You've mentioned a couple of times that you wondered why Interlisp version numbers on Unix files weren't the same as Emacs versions, and today I happened to look at what Emacs does --

26.1.3 Making and Deleting Numbered Backup Files
If a file's name is foo, the names of its numbered backup versions are foo.~v~, for various integers v, like this: foo.~1~, foo.~2~, foo.~3~, ...,foo.~259~, and so on.

so we're using the same format for file versions -- but what we're NOT doing like emacs is that we treat foo as equivalent to foo.~1~, while emacs treats the unversioned name as the "real" version, and .~1~ as the backup representing the old version.

I suspect that originated in matching the IFS behavior where it wasn't an issue of numbered "backup" versions, but every file had a version number and if there was only one it was .;1

-- Nick

The emacs method doesn't require a file system supporting hard links, or preserving them through folder sharing or git.
The DSK.c code seems to recover fine with it finds unlinked version.
. It isn’t a problem on read, but when you’re writing a new file it gives an error.

[masinter]

looks like the CMLSMARTARGS in venuelispcore.zip had a similar problem with CMLSMARTARGS.~3~ a duplicate of CMLSMARTARGS.~2~ and CMLSMARTARGS.~4~ and CMLSMARTARGS (with no version) empty.

[masinter]

Most of the discussion is about how Interlisp {DSK} works, and not about the subject title.
There was a github and versions back a while ago but I will mark this as Won't Fix.