This is essentially a revert of 25d86e8e5d
The primary motivation for this is so that paths beginning with `../`
don't get reformatted to begin `./../`.
The secondary motivation for this is to more closely match the standard.
There are fewer special cases in the logic if there is a dedicated
constructor for the `Parent` case.
This begins updates the filesystem layout for the tests to match
the new layout from the standard test suite (See:
https://github.com/dhall-lang/dhall-lang/pull/265)
This is still missing a part of the standard requirement, which is checking
parsing and import test results against an expected output (instead of
just checking that they succeed). I plan to add that in a subsequent
pull request. This is mainly to unblock other features that require using
the new standard layout.
