.gitattributes export-subst doesn't work correctly

[Warr1024]

Summary

.gitattributes export-subst are not being handled at all by git-export-all (upstream issue https://github.com/Kentzo/git-archive-all/issues/81). No progress on this is evident, and the git-export-all author's approach of having to recreate all git features is ultimately doomed to suffer more of these sorts of issues in the future.

As a workaround, we should at least allow use of plain git exports when the package doesn't contain any submodules, as probably applies to most packages, and especially to the ones I know are affected (the NodeCore ones).

Steps to reproduce

1. Create a release for NodeCore or NodeCore Alpha (or look at any of the releases already on CDB).
2. Run the game and open up the "inventory" screen (about dialog).

Expected:

The version number of the release is listed. These are calculated from a version.lua file that has git export substitutions in it to access the commit metadata at export time.

Observed:

The version is listed as "development/contentdb version" because the substitutions weren't performed.

[doxygen-spammer]

Would it help to convert submodules to subtrees before archiving?

Quick internet search yielded: https://stackoverflow.com/questions/28215244/convert-git-submodule-to-subtree

Then git archive can be used instead of git-archive-all, which would fix this issue, #184, and any future changes to git at the same time.

I just learned today about the existence of git subtree, and immediately tried this. I can not give a definitive recommendation therefore.