Move "From Cursor" operator which sets dupli group offset to own operator

Previously it used to use cursor location from time when panel was drawn,
which in some cases lead to using previous cursor location instead of current.

release/scripts/startup/bl_ui/properties_object.py

@@ -162,7 +162,6 @@ class OBJECT_PT_groups(ObjectButtonsPanel, Panel):
 
         # XXX, this is bad practice, yes, I wrote it :( - campbell
         index = 0
-        value = str(tuple(context.scene.cursor_location))
         for group in bpy.data.groups:
             if ob.name in group.objects:
                 col = layout.column(align=True)
@@ -181,9 +180,8 @@ class OBJECT_PT_groups(ObjectButtonsPanel, Panel):
                 col = split.column()
                 col.prop(group, "dupli_offset", text="")
 
-                props = col.operator("wm.context_set_value", text="From Cursor")
-                props.data_path = "object.users_group[%d].dupli_offset" % index
-                props.value = value
+                props = col.operator("object.dupli_offset_from_cursor", text="From Cursor")
+                props.index = index
                 index += 1