Running Overlord on multiple Lisp processes (machines?)

[ruricolist]

Overlord handles parallel builds with Lisp threads, but not between multiple Lisp instances. Two things need to happen to make this possible:

1. Write a portable file-locking library (the Windows part is already done).
2. Rewrite the database as a protocol that supports different backends, and add support for an external backend (e.g. SQLite).

[ruricolist]

On further thought, it would probably be better to coordinate file access through the database and not bother with OS-level file locking. Especially if we want to generalize to running on multiple machines.