implicit commits

[dimitri-yatsenko]

MySQL commits the ongoing transaction when a data definition command is issued.
https://dev.mysql.com/doc/refman/5.7/en/implicit-commit.html

DataJoint declares tables on the fly and a table may get declared during a transaction, triggering an implicit commit, causing anomalous behavior.

For example, when a table attempts to populate its subtable that has not yet been declared, the first insert into the subtable will trigger its declaration and an implicit commit of the incomplete transaction.

[dimitri-yatsenko]

Fixed in #72