#15 Page state is not properly cleared

[Paul Speed]

Right now, once the next and previous buttons have been
activated then the page init will not be called
properly. Furthermore, it seems that since these
values aren't refreshed that existing state could cause
weird behavior (like starting on the wrong page and so on).

The SetDlgResponseList call needs to reinitialize these
state variables. Also, for several use-cases it would
be nice to do this refresh during SetDlgPageInt as well.

Recommend:
-add a function for manually clearing the state
-have the SetDlgResponseList and SetDlgPageInt calls
automatically call this (potentially make it optional
in SetDlgPageInt)