[lmi] help for individual wxRadioBox items

[Vadim Zeitlin]

 Hello,

 After tooltips, we're working on implementing support for specifying the
help text for the individual radio box items. Just to be sure that we are
doing what's needed for lmi I'd like to briefly summarize the upcoming
changes:

1. wxRadioBox::SetItemHelpText(n, text) will be added
2. wxRadioBox XRC handler will be modified to recognize "help" attribute
   on the <item> tags
3. wxRadioBox will handle F1/"?" button as expected, i.e. will show help
   for the currently selected item/item under mouse

 Please let me know if there are any problems with the above plan, thanks
in advance!
VZ