Add equality to drectangle

This is in the main dlib source code (rather than specifically
Python). Equality operators were missing for drectangles and
so were copied from rectangle.

dlib/geometry/drectangle.h

@@ -195,6 +195,19 @@ namespace dlib
             return *this;
         }
 
+        bool operator== (
+            const drectangle& rect
+        ) const
+        {
+            return (l == rect.l) && (t == rect.t) && (r == rect.r) && (b == rect.b);
+        }
+
+        bool operator!= (
+            const drectangle& rect
+        ) const
+        {
+            return !(*this == rect);
+        }
 
     private:
         double l;

dlib/geometry/drectangle_abstract.h

@@ -319,6 +319,25 @@ namespace dlib
                 - returns #*this
         !*/
 
+        bool operator== (
+            const drectangle& rect
+        ) const;
+        /*!
+            ensures
+                - if (top() == rect.top() && left() == rect.left() &&
+                      right() == rect.right() && bottom() == rect.bottom()) then
+                    - returns true
+                - else
+                    - returns false
+        !*/
+
+        bool operator!= (
+            const drectangle& rect
+        ) const;
+        /*!
+            ensures
+                - returns !(*this == rect)
+        !*/
     };
 
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