Properly detect and test mysql v3 default JOIN behavior

While investigating how to rewrite the rather useless 39712b481, it became
clear that not only can the test be performed offline, but that there is
already a pseudo-test due to sqlite's version of 3.x.y being mistaken for
MySQL 3

Properly fix the test to check behavior on both versions 3 and 4, and in the
process fix a potential bug of a stale sqlmaker when a reconnect cycle takes
place against a *different* physical rdbms (which btw makes me realize another
problem with trying to do mixed-environment replication... sigh)