Submodule update on windows

Updating the vsi_common submodule from just on windows, will cause git to error if it tries to rewrite the just file itself, as it is in use, and Windows doesn't support this like *nix does.

The result is a horrible explosion of a partially checked out vsi_common repo, in a dirty state, that takes both a git reset --hard and git clean df, followed by a manual update.

Possible solutions:

1. Someway to detangle using the just file on windows, an exec to a tmp file?
   • setup.env could define the function just instead, that would source what is currently the file just
2. git hook on windows, to keep vsi_common up to date...
3. Detecting the problem before it happens, and echoing out that you need to git submodule update --recursive vsi_common manually

Start by inspecting the just file and setup.env, then reproduce the Windows submodule update path involving git. Done means updating vsi_common on Windows no longer leaves a partially checked-out dirty repository, or detects the condition and clearly directs the manual recursive update.