Transactions being wrongly shared across requests in tests

[calpaterson]

Description

Somewhere along the line, something has gone wrong and the session lifetime in tests not crosses multiple requests

Steps to reproduce

1. Find a test that POSTs something and then GETs it
2. Remove the sesh.commit() from the relevant system code

Expected result

Test fails

Actual result

Test passes

Additional details

csvbase/csvbase/web/main/bp.py

Line 1199 in 67ed93c

sesh.commit()

is a good candidate, when run in conjunction with the registration tests