Another solution, which I've happily adopted, is: just use a database! I put all modules in an SQLite database, so if I want to constrain a module to use a spe

Another solution, which I've happily adopted, is: just use a database! I put all modules in an SQLite database, so if I want to constrain a module to use a specific version of another module, I just do it. It doesn't solve Unix's problem. But it does solve mine, and that's good enough for me.