- [feature] Calling rollback() within a

- [feature] Calling rollback() within a
session.begin_nested() will now only expire
those objects that had net changes within the
scope of that transaction, that is objects which
were dirty or were modified on a flush.  This
allows the typical use case for begin_nested(),
that of altering a small subset of objects, to
leave in place the data from the larger enclosing
set of objects that weren't modified in
that sub-transaction.  [ticket:2452]
- inline the "register_newly_XYZ" functions to operate
upon collections to reduce method calls