While adding unit tests for ExplodedImage (originally JDK-8355953), the following issues were found:

1. ExplodedImage is fundamentally untestable in it current form.
  - Necessary to fix for adding unit tests.

2. Package "link" nodes behave incorrectly
  - Current version incorrectly resolves trailing paths. This is deliberately coded, but incorrect behavior.

3. Missing override method results in broken "type" reporting.
  - A resource node currently returns "false" for *all* of the isXxxx() methods because "isResource()" is not overridden.

4. Needless use of ConcurrentHashMap.
  - Apart from close(), every map access is already synchronised, so HashMap would suffice and be faster.

5. Incorrect logic around module paths.
  - A mistake in logic allows the path "/modules/" to resolve to a node. This is an edge case only caught with targeted unit tests.

6. Nodes can be created for non-file filesystem objects.
  - Nodes should only exist for plain files or directories. Currently a resource node could be created for device files or symbolic links.

Issues 1-3 are important, but 4-6 seem worth fixing while work is being done on the class.