Fix #363 by correctly doing the wxFrame/wxPanel parenting

As far as I understand, a wxFrame needs a wxPanel child, but we shouldn't
reparent this wxPanel to some other container. As a consequence, I created an
initial wxPanel for the gwindow wxFrame and assigned it the previous sizer
(instead of using the gviz panel as the wxFrame's panel).
Not sure why it wasn't segfaulting on my other systems, though.

printrun/gviz.py

@@ -26,10 +26,11 @@ class window(wx.Frame):
         self.CreateStatusBar(1);
         self.SetStatusText("Layer number and Z position show here when you scroll");
 
-        self.p = gviz(self, size = size, build_dimensions = build_dimensions, grid = grid, extrusion_width = extrusion_width)
+        panel = wx.Panel(self, -1)
+        self.p = gviz(panel, size = size, build_dimensions = build_dimensions, grid = grid, extrusion_width = extrusion_width)
 
         vbox = wx.BoxSizer(wx.VERTICAL)
-        toolbar = wx.ToolBar(self, -1, style = wx.TB_HORIZONTAL | wx.NO_BORDER)
+        toolbar = wx.ToolBar(panel, -1, style = wx.TB_HORIZONTAL | wx.NO_BORDER)
         toolbar.AddSimpleTool(1, wx.Image(imagefile('zoom_in.png'), wx.BITMAP_TYPE_PNG).ConvertToBitmap(), 'Zoom In [+]', '')
         toolbar.AddSimpleTool(2, wx.Image(imagefile('zoom_out.png'), wx.BITMAP_TYPE_PNG).ConvertToBitmap(), 'Zoom Out [-]', '')
         toolbar.AddSeparator()
@@ -41,7 +42,7 @@ class window(wx.Frame):
         toolbar.Realize()
         vbox.Add(toolbar, 0, border = 5)
         vbox.Add(self.p, 1, wx.EXPAND)
-        self.SetSizer(vbox)
+        panel.SetSizer(vbox)
         self.SetMinSize(self.ClientToWindowSize(vbox.GetMinSize()))
         self.Bind(wx.EVT_TOOL, lambda x:self.p.zoom(200, 200, 1.2), id = 1)
         self.Bind(wx.EVT_TOOL, lambda x:self.p.zoom(200, 200, 1/1.2), id = 2)