Endpoints can be explicitly marked as `save_session=False` (default is
true across the board). In that case they will have an in-memory session
(either the existing one or a brand new one) but the session won't be
persisted to disk.
Currently used for non-browser RPC endpoints: the APIs don't use
cookies/sessions and we can't assume the RPC libraries keep cookies
across calls. This means a new session is created and saved to disk for
each RPC calls, for no useful reason.
Christophe Simonis
f65528a74e