Add missing sip bindings

Author: nyalldawson

python/core/qgsexpression.sip

@@ -176,6 +176,22 @@ class QgsExpression
      */
     void setDistanceUnits( QGis::UnitType unit );
 
+    /** Returns the desired areal units for calculations involving geomCalculator(), eg "$area".
+     * @note areas are only converted when a geomCalculator() has been set
+     * @note added in QGIS 2.14
+     * @see setAreaUnits()
+     * @see distanceUnits()
+     */
+    QgsUnitTypes::AreaUnit areaUnits() const;
+
+    /** Sets the desired areal units for calculations involving geomCalculator(), eg "$area".
+     * @note areas are only converted when a geomCalculator() has been set
+     * @note added in QGIS 2.14
+     * @see areaUnits()
+     * @see setDistanceUnits()
+     */
+    void setAreaUnits( QgsUnitTypes::AreaUnit unit );
+
     /** This function currently replaces each expression between [% and %]
      * in the string with the result of its evaluation on the feature
      * passed as argument.