7050358: (fs spec) Path.toUri doesn't allow custom providers to use opaque URIs.

[Alan Bateman]

This is a spec bug that came up the nio-discuss list in the last week. 
Path's toUri method currently specifies that the method returns a 
hierarchical URI but this prevents custom providers from using opaque 
URIs. It should have specified that the URI is absolute. The demo zip 
provider that we have in jdk7 falls foul of this because it uses the 
legacy JAR URL syntax which are opaque. The webrev with the change to 
fix this is here:

http://cr.openjdk.java.net/~alanb/7050358/webrev/

I have a reviewer, and I hope to get this into jdk7 soon.

-Alan