Invalidate the cached best size whenever something changes that could affect the best size

git-svn-id: http://svn.wxwidgets.org/svn/wx/wxPython@73340 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Use Activate instead of Show

git-svn-id: http://svn.wxwidgets.org/svn/wx/wxPython@73341 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Invalidate the cached best size whenever something changes that could affect the best size

git-svn-id: http://svn.wxwidgets.org/svn/wx/wxPython@73342 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775