0.12.2dev: in session handling, try to avoid table deadlocks (#9705)  - in `Session.save`, split `save_session` transaction in two (actually save the session, then eventually purge the expired sessions)  - always access tables in the same order, first `session`, then `session_attribute`
0.12.2dev: in session handling, try to avoid table deadlocks (#9705)
 - in `Session.save`, split `save_session` transaction in two (actually save the session, then eventually purge the expired sessions)
 - always access tables in the same order, first `session`, then `session_attribute`

git-svn-id: 30ec3c1a2098df185a8733d0352d646269562639@10459 af82e41b-90c4-0310-8c96-b1721e28e2e2

exocad/exotrac,exocad/exotrac,exocad/exotrac,exocad/exotrac