[web] fix AbstractSessionManager.clean_sessions (closes #5757240) sessions were not closed if "last_usage_time = session.cnx.check()" actually raises an AtributeError.

[migration/3.21] ask fewer questions Several questions per table is just unreasonable.

[server] typo fix

[test] check that we reject an rqlexpression in computed relation perms

Fix (de)serialization of ComputedRelation read permissions For normal relation types, permissions don't need to be stored since they're just default values for the relation definitions. However, computed relations are serialized (as CWComputedRType), while their relation definitions are added at schema finalization time, and are only in memory. So add the 'read_permission' relation to CWComputedRType, and the appropriate hooks to save and restore those permissions. To avoid having to touch yams, we drop the 'add' and 'delete' permissions from the default computed relation permissions; this should probably be backported there. The actual permissions (set on the relation definitions) are hardcoded in finalize_computed_relations anyway. In deserialize_schema, the CWComputedRType handling needs to be delayed a little bit, until after we've called deserialize_ertype_permissions. The rql2sql test is adjusted because CWComputedRType has a 'name' attribute and the 'read_permission' relation, which generates ambiguity vs CWEType. We add an explicit CubicWebRelationSchema.check_permission_definitions, since we need to check both that computed and non-computed rtypes are defined properly. Based on report and initial patch from Christophe de Vienne (thanks!). Closes #5706307

Copy read permissions on ComputedRelation rdefs Closes #5694110

[datafeed] fix typo in DataFeedXMLParser.is_deleted (closes #5729755)

[server/sources] make sure entity._cw is a Connection before calling Storages The storage callbacks don't get an explicit Connection objects, so they go through entity._cw to access the repo and schedule operations. Since that entity object comes out of the entity cache, its _cw may be a web request instead of a Connection. So fix it up around the storage callbacks. Closes #5753543

[hooks] base64-encode extid before inserting it into moved_entities If we insert the wrong value we're never going to find these entities again... Closes #5741105.

[hook] remove assumption about entity cache vs cw_edited We were assuming that if an entity is in the connection's cache, it has a cw_edited attribute. This doesn't seem to always be the case. At least in cubicweb 3.21, merging the web and repo-side caches makes this more likely, but Denis says he's also seen this on 3.20.