[7u] Request for approval: 8015016 : Improve JAXP 1.5 error message

[huizhe wang]

Hello,

This is a straight backport from 8, the changes are identical.

Bug: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=8015016
Review thread: 
http://mail.openjdk.java.net/pipermail/core-libs-dev/2013-June/017746.html
Changeset: http://hg.openjdk.java.net/jdk8/tl/jaxp/rev/c2957e596bee

Thanks,
Joe