Consult history in fileloader.

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.

pkg/commands/edit/add/configmap.go

@@ -67,7 +67,7 @@ func newCmdAddConfigMap(fSys fs.FileSystem, kf ifc.KunstructuredFactory) *cobra.
 			}
 
 			// Add the flagsAndArgs map to the kustomization file.
-			kf.Set(fSys, loader.NewFileLoader(fSys))
+			kf.Set(fSys, loader.NewFileLoaderAtCwd(fSys))
 			err = addConfigMap(kustomization, flagsAndArgs, kf)
 			if err != nil {
 				return err