JDK 9 change to symlink handling causes misleading class.public.should.be.in.file diagnostic

see: http://mail.openjdk.java.net/pipermail/compiler-dev/2017-April/010892.html

JDK 9 changes how javac handles symlinks, and causes misleading diagnostics for public class declarations that don't match the name of the symlink target.

$ echo 'public class Hello {}' > SOURCE
$ ln -s SOURCE Hello.java

$ javac -fullversion Hello.java
javac full version "1.8.0_152-ea-b02"
... OK

$ javac -fullversion Hello.java
javac full version "9-ea+163"
Hello.java:1: error: class Hello is public, should be declared in a file named Hello.java

The JDK 8 behaviour seems preferable, but if the more aggressive path canonicalization in JDK 9 is kept then the canonical path should also be used for the diagnostic.