improved check_thy: produce a checked theory_ref (thread-safe version); removed obsolete self_ref (cf. check_thy); thread-safeness: when creating certified items, perform Theory.check_thy *last*; eq_thy: no check here; marked some critical sections;
improved check_thy: produce a checked theory_ref (thread-safe version);
removed obsolete self_ref (cf. check_thy);
thread-safeness: when creating certified items, perform Theory.check_thy *last*;
eq_thy: no check here;
marked some critical sections;

MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle