minor symmetry breaking for codatatypes like llist

fix bug with mutually recursive and nested codatatypes

fix minor bug in sym breaking

modernized specifications; tuned headers;

Document_Model: include token marker here;

tuned;

misc tuning -- produce reverse_edits at most once (note that foldRight produces a reversed list internally, while recursion is infisible due to small stack vs. large stack frames on JVM);

editor mode;

Text_Edit.convert/revert;

renamed to_current to convert, and from_current to revert;

Change.Snapshot: include from_current/to_current here, with precomputed changes;

explicit Change.Snapshot and Document.Node; misc tuning and clarification; Document_View: explicitly highlight outdated command status;

simplified/refined document model: collection of named nodes, without proper dependencies yet; moved basic type definitions for ids and edits from Isar_Document to Document; removed begin_document/end_document for now -- nodes emerge via edits; edits refer to named nodes explicitly;

somewhat uniform Thy_Header.split_thy_path in ML and Scala;

uniform naming of imports (source specification) vs. parents (thy node names) vs. parent_thys (theory values);

load_thy/after_load: explicit check of parent theories, which might have failed to join proofs -- avoid uninformative crash via Graph.UNDEF;

export use_thys_wrt;

more precise CRITICAL sections, using NAMED_CRITICAL uniformly;

updated to Netbeans 6.9;

schedule_futures: discontinued special treatment of non-parallel proofs, which might have affected memory usage at some point, but does not seem to make a difference with as little as 2GB RAM;

more precise CRITICAL sections; tuned;

removed unused Update_Time data (cf. ac94ff28e9e1);

modernized specifications; tuned headers;

eliminated Thy_Info.thy_ord, which is not really stable in interactive mode, since it depends on the somewhat accidental load order;

find_and_undo: no need to kill_thy again -- Thy_Info.toplevel_begin_theory does that initially (cf. 3ceccd415145);

renamed funny Library ROOT files back to default ROOT.ML -- ML files are no longer located via implicit load path (cf. 2b9bfa0b44f1);

tuned headers -- more precise load path;

theory loading: only the master source file is looked-up in the implicit load path;

load_thy: refer to physical master directory (not accumulated source import directory) and enable loading files relatively to that;

simplified/clarified Thy_Load path: search for master only, lookup other files relative to that; tuned;