fix DSK device to deal with non-linkable file system

[masinter]

some file systems don't support hard or symlinks, some only support symlinks.
shared folders in VirtualBox
Dropbox

Seems like DSK code has some problems with creating new versions in the situation with ACODE;4

[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.

[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]

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.