As per the wx-dev discussion in early Jan, replaced

As per the wx-dev discussion in early Jan, replaced
wxWindow::m_parentSizer with m_containingSizer which is used to track
which sizer this window is a member of.  Windows will now remove
themselves from a sizer when destroyed.  Also added accessors so
window classes can find out if they are in a sizer and do things like
reset their min size, etc.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@14221 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775