Previously, if a JarFile was created from a directory nested inside
another jar file, it would look for the manifest in
pathFromRoot/META-INF/MANIFEST.MF. This is incorrect as, unlike a
JarFile created from a jar file, the archives are one and the same
so the manifests should be too.
This commit updates JarFile so that its aware of how it was created
(direct from a file, from a nested directory, from a nested jar). If
it was created from a file or from a nested jar, it uses its manifest.
If it was created from a nested directory, it uses the manifest of the
root archive.
Closes gh-5609
87de7e6382