IZPACK-1204 - UserInputPanel bug fixing sprint

This pull request addresses a couple of issues summarized in https://jira.codehaus.org/browse/IZPACK-1204 - UserInputPanel bug fixing sprint, which fixes:
* IZPACK-1205 UserInputPanel: displayHidden and readonly attribute flaws
* IZPACK-1203 UserInputPanel choice fields (radio, combo) with conditions on each don't use current condition state