[hooks/syncsession] try to remove cnx vs session confusion

Fix Binary.__eq__ (closes #4172701) Due to a typo we always returned true, which was unhelpful.

[dataimport] stop ignoring errors on flush That can only result in database corruption.

[dataimport] don't commit on flush Changeset 26cdfc6dd6f8 introduced this confusion for no apparent reason, and it doesn't make much sense.

[test] Add test for dataimport's RQLObjectStore

[dataimport] Stop swallowing errors from commit/flush Silent DB corruption is not OK. Also drop comment from ObjectStore.commit that I don't understand.

[dataimport] Update RQLObjectStore to Connection API Take a connection instead of a session. Don't play games with set_cnxset.

[dataimport] remove _rql heresy 1) ObjectStore knows nothing about rql, it just drops it on the floor 2) RQLObjectStore has a session, it can run rql that way 3) setting an object's "_rql" attribute is not a reasonable user-facing interface Also drop _commit attribute from base ObjectStore, it doesn't use it.

[dataimport] remove dead code The only caller of ObjectStore._put is ObjectStore.create_entity, which RQLObjectStore overrides (and doesn't call up).

[dataimport] do not use sys.exit() to raise missing argument error Related to #3845572

[dataimport] _create_copyfrom_buffer: add the tests Related to #3845572

[dataimport] _create_copyfrom_buffer: do not ignore columns if data is a list Related to #3845572