clean command broken in master - works in 3.3.6

[nixjdm]

Normally, clean would purge the build dir, now, it seems to not do anything. Even unreferenced artifacts I place in the build dir remain. This seems caused by recent changes from PR #203 in builder.py. @dairiki could you take a look?

prune(all=True), now returns an empty generator, instead of everything.

The test added in that PR is correct - in a lektor build, previously generated artifacts of sources that are now marked hidden to get pruned, but prune(all=True) fails.

[nixjdm]

Thanks!

[dairiki]

Yup, my fault!

This issue is that this should be a yield from self.iter_existing_artifacts() rather than a return.

Thank you for the report.