Do a longstanding TODO to remove kustomizationerror.
It wasn't used much, and it wasn't used consistently,
because it's complicated to decided when it's worth
proceeding to accumulate errors when one already knows
that one has a fatal error in the kustomization. Its
use was blocking refactoring for simplicity and making
tests harder to write.
Removing it lets us reinstate the cyclomatic complexity
check in KustTarget.
Also added more info to the affected error messages.
Fixes#366
To reproduce #366, add
```
bases:
- .
```
to `examples/helloWorld/kustomization.yaml`, attempt to build it, and enjoy the stack overflow.
This PR fixes this by adding history to file loaders,
allowing one to avoid cycles in overlay->base
relationships. To make entry points clearer, this PR
exposes only two public ways to make a fresh
(no-history) loader
* rooted at `/`
* rooted at the process's current working directory.
When making a new loader from an existing loader,
retaining history along an overlay trace, the only
allowed use is to go deeper into a file hierarchy, or
go up and over to a never before visited sibling. This
fix can probably be defeated by devious symbolic links.
