Produce

This release adds source position information to error messages to help with source-level debugging of Producefiles.

-u` now takes a PATTERN so you can prevent the re-building of many targets with a single instance of the option.

Supersedes the previous botched release, which had the wrong version number in setup.cfg.

This release improves the behavior of the prelude

The Python code in the `prelude` attribute of the global section is now executed raw, before any expansions are done. Expansions in the prelude are probably not very useful, as dynamic substitutions can be done easily and way more flexibly in the Python code itself. Conversely, the change means that you can now finally use names defined in the prelude in expansions in the global section, which should have many uses.

Slightly better debugging of rule nonmatches

Fixes a lock contention issue introduced in the previous fix for a deadlock issue.