Fix behaviour of commit.
It's now a fatal error if the option to --logfile isn't readable.
Ditto if both --message and --logfile are specified.
transaction abort!
rollback completed
abort: impossible time zone offset: 4444444
transaction abort!
rollback completed
abort: invalid date: '1\t15.1'
transaction abort!
rollback completed
abort: invalid date: 'foo bar'
transaction abort!
rollback completed
abort: invalid date: ' 1 4444'
transaction abort!
rollback completed
abort: date exceeds 32 bits: 111111111111