Try harder to set the requester splitter position in wxSplitterWindow.

Try harder to set the requester splitter position in wxSplitterWindow.

The code in wxSplitterWindow tried to remember the requested position and set
the real sash position to it later, even if the initial window size was too
small to allow for it, but it didn't work because the requested position was
forgotten after the first size event, even though it was quite possible that
this event didn't really change the window size from the initial, small, one.

Try to make this more robust by ignoring the size events which don't really
change the window size. Also set m_lastSize correctly initially.

Now setting the sash position does work even if the splitter itself is inside
nested sizers (which results in many size events).

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68876 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775