Consistently declare wxCursor(wxImage) ctor when wxUSE_IMAGE==1

wxGTK already did it like this, but also only declared ctor not taking
wxImage in this case, while wxMSW and wxMac declared this ctor in any
case, even when wxUSE_IMAGE==0, but didn't define it then.

This doesn't matter much anyhow, as the build with wxUSE_IMAGE==0 is
clearly broken and these changes are not enough to fix it, but be at
least somewhat consistent and:

1. Don't declare methods using a class which is not available at all.
2. Do define methods using wxImage only internally, even if they do
   nothing when it's not available.

No real changes.

include/wx/gtk/cursor.h

@@ -25,10 +25,10 @@ public:
 #endif
 #if wxUSE_IMAGE
     wxCursor( const wxImage & image );
+#endif // wxUSE_IMAGE
     wxCursor(const wxString& name,
              wxBitmapType type = wxCURSOR_DEFAULT_TYPE,
              int hotSpotX = 0, int hotSpotY = 0);
-#endif
     wxCursor( const char bits[], int width, int height,
               int hotSpotX = -1, int hotSpotY = -1,
               const char maskBits[] = NULL,

include/wx/msw/cursor.h

@@ -19,7 +19,9 @@ class WXDLLIMPEXP_CORE wxCursor : public wxCursorBase
 public:
     // constructors
     wxCursor();
+#if wxUSE_IMAGE
     wxCursor(const wxImage& image);
+#endif // wxUSE_IMAGE
     wxCursor(const wxString& name,
              wxBitmapType type = wxCURSOR_DEFAULT_TYPE,
              int hotSpotX = 0, int hotSpotY = 0);

include/wx/osx/cursor.h

@@ -19,7 +19,9 @@ class WXDLLIMPEXP_CORE wxCursor : public wxCursorBase
 public:
     wxCursor();
 
+#if wxUSE_IMAGE
     wxCursor(const wxImage & image) ;
+#endif // wxUSE_IMAGE
     wxCursor(const wxString& name,
              wxBitmapType type = wxCURSOR_DEFAULT_TYPE,
              int hotSpotX = 0, int hotSpotY = 0);

include/wx/qt/cursor.h

@@ -22,10 +22,10 @@ public:
 #endif
 #if wxUSE_IMAGE
     wxCursor( const wxImage & image );
+#endif // wxUSE_IMAGE
     wxCursor(const wxString& name,
              wxBitmapType type = wxCURSOR_DEFAULT_TYPE,
              int hotSpotX = 0, int hotSpotY = 0);
-#endif
 
     virtual wxPoint GetHotSpot() const wxOVERRIDE;
     QCursor &GetHandle() const;

src/gtk/cursor.cpp

@@ -72,7 +72,6 @@ wxCursor::wxCursor()
 {
 }
 
-#if wxUSE_IMAGE
 wxCursor::wxCursor(const wxString& cursor_file,
                    wxBitmapType type,
                    int hotSpotX, int hotSpotY)
@@ -88,13 +87,15 @@ wxCursor::wxCursor(const wxString& cursor_file,
         img.SetOption(wxIMAGE_OPTION_CUR_HOTSPOT_Y, hotSpotY);
 
     InitFromImage(img);
+#endif // wxUSE_IMAGE
 }
 
+#if wxUSE_IMAGE
 wxCursor::wxCursor(const wxImage& img)
 {
     InitFromImage(img);
 }
-#endif
+#endif // wxUSE_IMAGE
 
 wxCursor::wxCursor(const char bits[], int width, int height,
                    int hotSpotX, int hotSpotY,

src/osx/carbon/cursor.cpp

@@ -225,12 +225,12 @@ wxCursor::wxCursor()
 {
 }
 
+#if wxUSE_IMAGE
 wxCursor::wxCursor( const wxImage &image )
 {
-#if wxUSE_IMAGE
     CreateFromImage( image ) ;
-#endif
 }
+#endif // wxUSE_IMAGE
 
 wxGDIRefData *wxCursor::CreateGDIRefData() const
 {

src/qt/cursor.cpp

@@ -59,11 +59,11 @@ public:
 wxIMPLEMENT_DYNAMIC_CLASS(wxCursor, wxGDIObject);
 
 
-#if wxUSE_IMAGE
 wxCursor::wxCursor(const wxString& cursor_file,
                    wxBitmapType type,
                    int hotSpotX, int hotSpotY)
 {
+#if wxUSE_IMAGE
     wxImage img;
     if (!img.LoadFile(cursor_file, type))
         return;
@@ -75,13 +75,15 @@ wxCursor::wxCursor(const wxString& cursor_file,
         img.SetOption(wxIMAGE_OPTION_CUR_HOTSPOT_Y, hotSpotY);
 
     InitFromImage(img);
+#endif // wxUSE_IMAGE
 }
 
+#if wxUSE_IMAGE
 wxCursor::wxCursor(const wxImage& img)
 {
     InitFromImage(img);
 }
-#endif
+#endif // wxUSE_IMAGE
 
 wxPoint wxCursor::GetHotSpot() const
 {