Compilation fix for PCH-less build after r74586.

Don't use wxWindow methods in wx/container.h, move AcceptsFocus()
implementation to containr.cpp.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74588 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775