RFR: JDK-8246353: Sealed types not supported by jshell

[Jan Lahoda]

Hi,

JShell does not support sealed types yet, this patch attempts to solve 
it. This patch:
-adds "permits" clauses to header dependencies of the class that defines 
it (so that JShell correctly detects the permitted classes must be added 
before the class is defined)
-JShell will not clear the final modifier, on any element (class, 
method, variable) before compiling the snippet
-javac will not report the "no sealed superclass" error for cases like:
non-sealed class I extends Undefined {}
(this makes support for non-sealed in JShell much easier, and is the 
right thing to do, I believe.)

Proposed webrev:
http://cr.openjdk.java.net/~jlahoda/8246353/webrev.00/

JBS: https://bugs.openjdk.java.net/browse/JDK-8246353

How does this look?

Thanks,
    Jan