fix #453 scrolling after radiogroup change from keyboard

When changing selected item in a radio group using keyboard arrows,
default action was not prevented, hence page might have scrolled if
scrollbars were present.

Close #490.
fix #504 failing test in Firefox 3.6

1) MultiSelect test was failing due to lack of support for `parentNode`
2) IOTest was failing due to a bug in Fx3.6 which when issuing HEAD
request reuses cached response from POSTs and preserves nonempty response value
of them.
just a commit
another commit