not using session contents iterators after session switch

[ichthyo]

Any attempt to use a session contents discovery iterator after closing/switching the session will cause a segfault. According to the current session lifecycle draft, the assumption is that any facilities actively using the session (i.e. engine, GUI, scripts) will be halted and cleared on a case-by-case base, before the session switch happens. Thus there seems to be no need for an explicit protection mechanism (which could be built into PlacementIndexQueryResolver).

verify this assumption holds and no access is possible after the session switch...