Add wxCursor ctor from XPM data to all ports

This just uses the existing wxImage ctor from XPM data and wxCursor ctor
from wxImage, but will allow the code creating cursors from XPM to still
work even when wxImage ctor from XPM is made explicit.

Add a trivial test just to check that the new ctor can be used.

include/wx/motif/cursor.h

@@ -32,6 +32,7 @@ public:
 
 #if wxUSE_IMAGE
     wxCursor(const wxImage& image);
+    wxCursor(const char* const* xpmData);
 #endif
 
     wxCursor(wxStockCursor id) { InitFromStock(id); }
@@ -52,6 +53,10 @@ protected:
 private:
     void InitFromStock(wxStockCursor);
 
+#if wxUSE_IMAGE
+    void InitFromImage(const wxImage& image);
+#endif
+
     void Create(const char bits[], int width, int height,
                 int hotSpotX = -1, int hotSpotY = -1,
                 const char maskBits[] = NULL);