RFR (JAXP) 8156845: Uri is getting incorrectly unwrapped

[huizhe wang]

Hi,

This patch fixes a missing feature in CatalogUriResolver where an uri 
entry can be referenced by a publicid (urn:publicid), similar to that of 
the public entry. The fix then is basically sharing the process for a 
public entry.

JBS: https://bugs.openjdk.java.net/browse/JDK-8156845
webrev: http://cr.openjdk.java.net/~joehw/jdk9/8156845/webrev/

Thanks,
Joe