This class requires wxTaskBarButton to be really implemented, so there is no
need to even define the MSW-specific version of it if wxUSE_TASKBARBUTTON is 0
anyhow.
This fixes a compilation problem with wxUSE_TASKBARBUTTON==0 but, more
importantly, just makes more sense.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@77745 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
First of all, do define it under non-MSW platforms.
Second, don't crash in it when running under XP where wxTaskBarButton is not
available.
Also add IsAvailable() method to check for its availability explicitly and add
a demonstration of this class to the dialogs sample.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@77706 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
