RFR 8247456: JShell: Handling of top-level final, abstract, and static modifiers

[Robert Field]

Please review --

Issue:

https://bugs.openjdk.java.net/browse/JDK-8247456

Webrev:

http://cr.openjdk.java.net/~rfield/8247456v0.webrev/

Allows the pasting of abstract methods, by pre-corralling them. This 
allows reference before defined.

Better handling of abstract on var errors.

Ignores "static" modifier, without annoying warning.

Final portion handled by sealed types fix.

-Robert