Add equality operators to wxItemAttr

It can be necessary to compare two item attributes for equality, e.g. to check
if the attributes have changed, so provide a straightforward implementation of
equality and inequality operator for it.

interface/wx/itemattr.h

@@ -35,6 +35,16 @@ public:
                const wxColour& colBack,
                const wxFont& font);
 
+    /**
+        Compare two item attributes for equality.
+    */
+    bool operator==(const wxItemAttr& other) const;
+
+    /**
+        Compare two item attributes for inequality.
+    */
+    bool operator!=(const wxItemAttr& other) const;
+
     /**
         Returns the currently set background colour.
     */