make IsEnabled() return false even if the window parent, and not the window itself, is disabled and added IsThisEnabled() implementing the old IsEnabled() behaviour; also significantly simplify the window state management code in all ports by factoring out the common parts in wxWindowBase

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@45031 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk1/bmpbuttn.cpp

@@ -202,7 +202,7 @@ void wxBitmapButton::OnSetBitmap()
     InvalidateBestSize();
 
     wxBitmap the_one;
-    if (!m_isEnabled)
+    if (!IsThisEnabled())
         the_one = m_bmpDisabled;
     else if (m_isSelected)
         the_one = m_bmpSelected;