elua: new util: table.uniq, and use it in xgettext generator

src/bin/elua/core/util.lua

@@ -366,4 +366,17 @@ M.find_file = function(fname, paths)
     end
 end
 
+-- table utils
+
+table.uniq = function(tbl)
+    local ret  = {}
+    local used = {}
+    for i, v in ipairs(tbl) do
+        if not used[v] then
+            ret[#ret + 1], used[v] = v, true
+        end
+    end
+    return ret
+end
+
 return M

src/bin/elua/modules/xgettext/generator.lua

@@ -69,6 +69,9 @@ local gen_grouped_messages = function(ps)
         end
         msg = ps()
     end
+    for i, msg in ipairs(ret) do
+        msg.flags = table.uniq(msg.flags)
+    end
     return ret
 end