Migration: fail if migration contains more than one query #373
Description
If a migration contains more than one query, such as a migration that adds a new column to a table, and then immediately adds a foreign key to that new column, the migration should FAIL.
This is because, if the first part of the migration succeeds, and the second part fails, the migration will not have been recorded to have ran successfully, yet the first half of the operation did actually succeed - leaving the database out of integrity.
This only needs to be done at the point of performing the migration, where currently we split the migration on the semicolon using a lexer.