Message11900

Oh, sorry; in https://hg.python.org/jython/rev/850f5980a2e3 I overlooked that `some_path` can have different meaning than `/some_path`. However fixing paths like `/C:/some_path` was still important. Apart from that I did not touch getJarFileNameFromURL implementation. It stems from older work. As part of #2386 I just moved it from another module to public API. Changing it to make better use of Java API is the best solution I suppose. Also simplifies its code a lot.

E.g.
java.io.File(
URL("jar:file:/C:/some_dir/some.jar!/a/package/with/A.class")
.openConnection().getJarFileURL().toURI())).getAbsolutePath()
should do it...