Keep current value if parent's trigger keeps it available

[dannyadair]

If a parent change triggers new choices, the current choice will be blanked even if it is available in the new choices. I think that is undesirable (and makes the change() mentioned in issue #1 a little more complicated).

[runekaagaard]

This is actually intentional, to prevent that the enduser forgets to set the correct value. But he can also forget what the correct value was, so I've changed my mind on this :) Accepted, and thx for your feedback!