Improve conversion between wxPaperSize and GtkPaperSize

Eliminates many "Gtk-WARNING **: Unknown paper size", and the occasional
"GLib-GObject-CRITICAL **: g_object_unref: assertion `G_IS_OBJECT (object)' failed".
And fixes approximately one zillion memory leaks.


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@76270 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
fix more memory leaks

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@76271 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775