Update MANIFEST and provide a custom MANIFEST.SKIP

The MANIFEST.SKIP was seeded with an initial "#!include_default" and
`make manifest` step to grab the ExtUtils::Manifest defaults.

Running `make manifest` will now correctly manage MANIFEST.  This allows
`make distcheck` to function.
Revert "Correct documentation about right joins"

This reverts commit b5ea7e4e4eae7b535ea67474ebe940a207fb828a.

English parsing fail on my part.  Inner joins discard _any_ unmatched
records, regardless of which stream, and that's what the original
wording indeed said.