Added 'HasAlpha' attribute for wxColourProperty. Setting it to true allows user to edit the alpha component.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66520 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/propgrid/advprops.h

@@ -203,7 +203,8 @@ public:
         Override in derived class to customize how colours are printed as
         strings.
     */
-    virtual wxString ColourToString( const wxColour& col, int index ) const;
+    virtual wxString ColourToString( const wxColour& col, int index,
+                                     int argFlags = 0 ) const;
 
     /** Returns index of entry that triggers colour picker dialog
         (default is last).

include/wx/propgrid/property.h

@@ -697,6 +697,12 @@ wxPG_PROP_BEING_DELETED             = 0x00200000
 */
 #define wxPG_COLOUR_ALLOW_CUSTOM            wxS("AllowCustom")
 
+/**
+    wxColourProperty and its kind: Set to True in order to support editing
+    alpha colour component.
+*/
+#define wxPG_COLOUR_HAS_ALPHA               wxS("HasAlpha")
+
 /** @}
 */