src/Pure/Thy/sessions.scala
2016-03-30 ago tuned message;
2016-03-24 ago proper SHA1 digest as annex to heap file: Poly/ML reads precise segment length;
2016-03-16 ago support for Poly/ML heap hierarchy, which saves a lot of disk space;
2016-03-16 ago clarified signature;
2016-03-16 ago tuned signature;
2016-03-15 ago find heaps uniformly via Sessions.Store;
2016-03-15 ago clarified modules;
2016-03-15 ago clarified modules;