[webtest/pyviews] use the new connection api

[tests/sqlutils] use the new connection api

[tests/postgres] use the new connection api

[tests/repository] use the new connection api (part 2/2) Some notes: * module imports cleanup * the unimplemented `test_transaction_interleaved` is wiped

[repository,tests] use the new connection api (part 1/2) `add_info` should not play with the cnxset nor the mode. Static analysis showed that: * add_info is an internal api called with a non-none cnx.cnxset and also in write mode * only the altered test violated this assumption, which is now somewhat documented

[book] fix various parts of the rql section * syntax error * erroneous query * bad sphinx :func: usage

[repository] session -> cnx renaming (already done in the source object)

[tests/session] remove unused import

[tests/datafeed] use the new connection api

[tests/checkintegrity] use the new connection api * serverctl: the db-check command also uses an internal connection object, which makes more sense in the context of `checkintegrity`. * checkintegrity: rename srvcnx to just cnx (a bit because in the near future, there will be one cnx to rule them all)