Fix board rng to allow action tags

(transplanted from b79345dd5cccca43c6cd35dbb963432241c0d8a8)

trytond/ir/ui/board.rnc

@@ -142,6 +142,7 @@ attlist.xpath &= attribute expr { text }
 attlist.xpath &=
   [ a:defaultValue = "inside" ]
   attribute position { "inside" | "replace" | "replace_attributes" | "after" | "before" }?
-action |= notAllowed
+action = element action { attlist.action, empty }
+attlist.action &= attribute name { text }
 label |= notAllowed
 start = data | board | label

trytond/ir/ui/board.rng

@@ -438,8 +438,14 @@
       </attribute>
     </optional>
   </define>
-  <define name="action" combine="choice">
-    <notAllowed/>
+  <define name="action">
+    <element name="action">
+      <ref name="attlist.action"/>
+      <empty/>
+    </element>
+  </define>
+  <define name="attlist.action" combine="interleave">
+    <attribute name="name"/>
   </define>
   <define name="label" combine="choice">
     <notAllowed/>