We use the datatype representation from the globbing in cabal-install,
but preserve a standalone parser for globs present in cabal files, whose
specification is constrained by the cabal specification. The
implementations are merged taking the best parts of each.

We also make sure sdist is robust to accidentally-listed directories,
as the refactor of the globbing modules re-uncovered this issue, and
required a prompt fix for the refactor not to break some things.

Fixes #5349