Changes

Summary

1. merged
2. Added tag Isabelle2018-RC3 for changeset 71aa5a9128c2
3. proper return code (true) if file is absent;
4. clarified word syntax for the sake of control symbols, e.g. \<^term>;
5. updated to Poly/ML fixes-5.7.1 b3d1ff33a4b4;
6. more robust: do not defer potentially slow/big lazy facts to the very end;
7. more robust: potentially a workaround for spurious HOL build problems seen by Larry Paulson;
8. tuned;
9. eliminated non-monotomnic Lazy.is_pending: Result may return to Expr due to Interrupt;
10. unused;
11. removed junk;
12. clarified documentation;
13. added check_delay / check_limit for more robust treatment of structurally broken theory sources (or genuine non-termination);
14. proper adjust_maxidx: assms could have maxidx >= 0, e.g. from command "subgoal premises";
15. proper maxidx: if x does not occur in A, its maxidx could get lost;
16. tuned;
17. more flexible session selection as in "isabelle jedit";
18. updated to jdk-8u181;