Clearer error message

Currently, with a fixture that has an incorrect count of values, your test simply errors out with
"SQLSTATE[HY093]: Invalid parameter number: number of bound variables does not match number of tokens"

Some digging reveeled the issue in the insert() method.
With this PR the exception responds with "Count of fields does not match count of values"

We could make it say: "Fixure invalid: Count of fields does not match count of values" to be even more clear on the subject.