While the discussion about how to refactor test framework is not
finished (#1654), make this change: move `rm -rf build` in the
beginning of the test. For these reasons:
* it is useful to inspect the contents of the `build` directory
especially after the test failure
* if build crashes mid-test (e.g. process killed), next run should
not be affected by the `build` directory from the previous run
Until now namespaces were stored as (reversed) lists of strings.
It led to:
* confusing code where we work on the underlying representation of
namespaces rather than say what we mean (using `isSuffixOf` to mean
`isParentOf`)
* potentially introducing errors by not respecting the invariant cf.
bug report #616 (but also name generation in the scheme backend
although that did not lead to bugs as it was self-consistent AFAICT)
* ad-hoc code to circumvent overlapping interface implementation when
showing / pretty-printing namespaces
This PR introduces a `Namespace` newtype containing a list of strings.
Nested namespaces are still stored in reverse order but the exposed
interface aims to support programming by saying what we mean
(`isParentOf`, `isApproximationOf`, `X <.> Y` computes to `X.Y`, etc.)
irrespective of the underlying representation.
