prefer Nimbus look and feel on all platforms, instead of the somewhat ugly javax.swing.plaf.metal.MetalLookAndFeel, which presumably is implicit fall-back nonetheless;

edit_document: synchronous reply to ensure consistent state wrt. calling (AWT) thread;

distinguish proper Isabelle_Process INPUT vs. raw STDIN, tuned corresponding method names; asynchronous Isabelle_Process.init -- raw ML toplevel stays active; simplified Isabelle_Process using actors; misc tuning;