Allow "moving" wxX11Display objects

This is not a real move-ctor but std::auto_ptr<>-like "stealing" ctor. It
still allows to pass Display ownership to another function which is all that
is needed for our purposes.

include/wx/unix/utilsx11.h

@@ -67,6 +67,13 @@ public:
     wxX11Display() { m_dpy = XOpenDisplay(NULL); }
     ~wxX11Display() { if ( m_dpy ) XCloseDisplay(m_dpy); }
 
+    // Pseudo move ctor: steals the open display from the other object.
+    explicit wxX11Display(wxX11Display& display)
+    {
+        m_dpy = display.m_dpy;
+        display.m_dpy = NULL;
+    }
+
     operator Display *() const { return m_dpy; }
 
     // Using DefaultRootWindow() with an object of wxX11Display class doesn't