Make the preview frame float on parent by default.

Otherwise it is hidden when the parent is a modal dialog, at least under
wxGTK.

This is a backport of r58154 from trunk and closes #10341.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_8_BRANCH@62502 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/prntbase.h

@@ -370,8 +370,8 @@ public:
                    const wxString& title = wxT("Print Preview"),
                    const wxPoint& pos = wxDefaultPosition,
                    const wxSize& size = wxDefaultSize,
-                   long style = wxDEFAULT_FRAME_STYLE,
-                   const wxString& name = wxT("frame"));
+                   long style = wxDEFAULT_FRAME_STYLE | wxFRAME_FLOAT_ON_PARENT,
+                   const wxString& name = wxFrameNameStr);
     virtual ~wxPreviewFrame();
 
     void OnCloseWindow(wxCloseEvent& event);