[whatwg] Database storage and detecting success of COMMIT.

[Scott Hess]

If the statement to executeSql() is invalid, then an exception will be
raised immediately, which can be caught by wrapping the call to
executeSql() with an exception handler.  If there is an error in the
course of executing the statement, it will be exposed by the errorCode
in the callback.  If there is no such error, the callback will be
executed in the context of an implicit database transaction.  This
would appear to leave no place from which to detect an error
committing the transaction.  There is also no place to hang code to
execute when the transaction is known to be successful.

-scott