Changes to jrt file system provider in JDK 13

[Alan Bateman]

For those using the jrt file system provider then please make sure to 
test with the latest JDK 13 EA builds. One of the changes in JDK 13 is 
to fix issues encoding paths to files in the jrt file system as jrt URLs 
and vice versa [1]. The compatibility impact with fixing these issues is 
that it might expose cases where a tool is (perhaps unknowingly) using 
URLs that don't conform to the syntax documented in JEP 220. We've heard 
of one case where something is trying to create a URI to the /packages 
directory but that is a special directory for sym links and cannot be 
represented by a jrt URI.

-Alan

[1] https://bugs.openjdk.java.net/browse/JDK-8224946